build: add mamake strict level 4 (re: 1b0a4ff, 4eaf25c, 45feaa5)

Strict level 4 further tightens up the build system by implementing
the following changes:

1. Changes the syntax for recognising MAM variable expansions from
   ${...} to %{...}. The old sh-like ${...} form is now only
   recognised in strict level 3 and below, and is not treated
   specially in strict level 4. This allows the shell's ${...}
   syntax to be used in shell script actions without any risk of
   conflicts or confusion with MAM.

2. Disables my change from 45feaa5 that allows 'prev' to declare a
   simple file prerequisite in one line, with optional attributes,
   as an equivalent of an empty make...done block. It was confusing
   and not well designed to mix this with prev's original function:
   referencing a previously made rule.

3. Adds a 'makp' command that may now be used to declare a simple
   file prerequisite instead.

4. Gets rid of the 'implicit' attribute. It has never worked as
   documented! That functionality was simply not implemented.
   Instead, it was a simple equivalent of 'dontcare', which is
   certainly not what is wanted where 'implicit' was indicated.

src/cmd/INIT/mamake.c:
- Delete RULE_implicit symbol (the 'implicit' attribute) which,
  when used with 'make', had the same effect as RULE_dontcare.
- attributes(): Make 'implicit' attribute unavailable in strict
  level 4+; use RULE_dontcare for it otherwise.
- substitute():
  - Add %{ as the default prefix for MAM variable expansions. This
    is done regardless of strict level. The character combination
    %{ has never appeared in any Mamfile up to now, so there are no
    backward compatibility conerns, and this way, the new prefix
    can be used internally without complications.
  - Disable %{ at strict < 4.
  - For %{, disable special handling of ':', '=' and '['; these
    were just hacks to mitigate conflicts with sh/ksh syntax.
  - For %{, make it an error to expand an undefined variable when
    one of the two special expansion syntaxes is not used.
- make(): Add makp command. For backward compatibility with
  previous strict levels, it shares it code with prev, so the same
  block (somewhat refactored) continues to have both functions.
- Change internal expansions to use %{ instead of ${.

src/cmd/INIT/mkdeps.sh:
- Use %{ instead of ${ in generated dependencies.
- No longer emit the broken implicit attribute.
- For brevity, do not repeat rule name in 'done'.

**/Mamfile:
- Adapt to the new strict level 4, applying some slight refactoring
  where necessary. (The new strict level exposed one remaining
  dependency bug, in the generation of lc.h in libast/Mamfile,
  previously masked by the fact that 'implicit' was 'dontcare').

src/Mamfile

@@ -3,20 +3,20 @@ note * This build script is in an extended Make Abstract Machine (MAM)
 note * language. Documentation is at: src/cmd/INIT/README-mamake.md
 note *
 
-setv MAMAKE_STRICT 3
+setv MAMAKE_STRICT 4
 
 make install virtual
 	make all virtual
-		exec - ${MAMAKE} -r '*/*' ${MAMAKEARGS}
+		exec - %{MAMAKE} -r '*/*' %{MAMAKEARGS}
 	done
 	make announce_build_done virtual notrace
-		prev cmd/ksh93/ksh
-		exec - ${<} -c 'print "# KornShell $KSH_VERSION"'
+		makp cmd/ksh93/ksh
+		exec - %{<} -c 'print "# KornShell $KSH_VERSION"'
 		exec - echo "# Type 'bin/package use' to try it out"
 	done
 done
 
 make test virtual
 	exec - : testing KornShell $KSH_VERSION :
-	exec - ${MAMAKE} -r '*/*' ${MAMAKEARGS}
+	exec - %{MAMAKE} -r '*/*' %{MAMAKEARGS}
 done

src/cmd/INIT/Mamfile

@@ -3,7 +3,7 @@ note * This build script is in an extended Make Abstract Machine (MAM)
 note * language. Documentation is at: src/cmd/INIT/README-mamake.md
 note *
 
-setv MAMAKE_STRICT 3
+setv MAMAKE_STRICT 4
 setv INSTALLROOT ../../..
 setv CC cc
 
@@ -13,55 +13,61 @@ note *
 
 make install virtual
 	loop DIR bin include/ast lib/lib lib/probe/C/make lib/probe/C/pp lib/probe/C/mam
-		make ${INSTALLROOT}/${DIR}
-			exec - mkdir -p ${@}
+		make %{INSTALLROOT}/%{DIR}
+			exec - mkdir -p %{@}
 		done
 	done
 
 	note *
 	note * install helper scripts
 	note *
 
-	make probe.sh
-		prev C+probe
-		prev make.probe
-		exec - cat ${^} > ${@}
-	done
-	loop SCRIPT probe iffe mktest regress crossexec mkreq mkreq-maplib mprobe proto dylink mkdeps
-		make ${INSTALLROOT}/bin/${SCRIPT}
-			make ${SCRIPT}
-				prev ${@}.sh
-				exec - cp ${<} ${@} && chmod u+w,+x ${@}
+	make %{INSTALLROOT}/bin/probe
+		make probe
+			make probe.sh
+				makp C+probe
+				makp make.probe
+				exec - cat %{^} > %{@}
 			done
-			exec - cp -f ${<} ${@}
+			exec - cp %{<} %{@} && chmod u+w,+x %{@}
 		done
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/bin/mamprobe
+	loop SCRIPT iffe mktest regress crossexec mkreq mkreq-maplib mprobe proto dylink mkdeps
+		make %{INSTALLROOT}/bin/%{SCRIPT}
+			make %{SCRIPT}
+				makp %{@}.sh
+				exec - cp %{<} %{@} && chmod u+w,+x %{@}
+			done
+			exec - cp -f %{<} %{@}
+		done
+	done
+	make %{INSTALLROOT}/bin/mamprobe
 		note * the probe.sh dependency is needed for mamake to redo the probe when C+probe or make.probe is edited
 		prev probe.sh
-		prev mamprobe.sh
-		exec - cp ${<} ${@} && chmod u+w,+x ${@}
+		makp mamprobe.sh
+		exec - cp %{<} %{@} && chmod u+w,+x %{@}
 	done
 
 	note *
 	note * probe initialization
 	note *
 
-	make ${INSTALLROOT}/lib/probe/C/probe
+	make %{INSTALLROOT}/lib/probe/C/probe
 		prev C+probe
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/lib/probe/C/mam/probe
+	make %{INSTALLROOT}/lib/probe/C/mam/probe
 		prev mprobe
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/lib/probe/C/mam/mprobe
+	make %{INSTALLROOT}/lib/probe/C/mam/mprobe
 		prev mprobe
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/lib/probe/C/make/probe
+	make %{INSTALLROOT}/lib/probe/C/make/probe
 		prev probe
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
 	note *
 	note * check if -ldl is required
@@ -72,80 +78,80 @@ make install virtual
 	note *	 (3) dynamic progs built on irix 5.* and using -ldl fail
 	note *           at runtime on irix 6.* because -ldl is not there
 	note *
-	make ${INSTALLROOT}/lib/lib/dl
+	make %{INSTALLROOT}/lib/lib/dl
 		make dl.req
-			prev dl.c
-			exec - mkreq-maplib ${CC} : dl : ${^} : dl
+			makp dl.c
+			exec - mkreq-maplib %{CC} : dl : %{^} : dl
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
 	note *
 	note * requiring these is a botch
 	note *
-	make ${INSTALLROOT}/lib/lib/iconv
+	make %{INSTALLROOT}/lib/lib/iconv
 		make iconv.req
-			prev iconv.c
-			exec - mkreq-maplib ${CC} : iconv : ${^} : iconv
+			makp iconv.c
+			exec - mkreq-maplib %{CC} : iconv : %{^} : iconv
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/lib/lib/w
+	make %{INSTALLROOT}/lib/lib/w
 		make w.req
-			prev w.c
-			prev w2.c
-			exec - mkreq-maplib ${CC} : w : ${^} : w
+			makp w.c
+			makp w2.c
+			exec - mkreq-maplib %{CC} : w : %{^} : w
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
 	note *
 	note * miscellaneous -l* checks
 	note *
-	make ${INSTALLROOT}/lib/lib/intl
+	make %{INSTALLROOT}/lib/lib/intl
 		make intl.req
-			prev intl.c
-			exec - mkreq-maplib ${CC} : intl : ${^} : intl
+			makp intl.c
+			exec - mkreq-maplib %{CC} : intl : %{^} : intl
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/lib/lib/m
+	make %{INSTALLROOT}/lib/lib/m
 		make m.req
-			prev m.c
-			prev m2.c
-			prev m3.c
-			prev m4.c
-			prev m5.c
-			prev m6.c
-			exec - mkreq-maplib ${CC} : m : ${^} : m
+			makp m.c
+			makp m2.c
+			makp m3.c
+			makp m4.c
+			makp m5.c
+			makp m6.c
+			exec - mkreq-maplib %{CC} : m : %{^} : m
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
-	make ${INSTALLROOT}/lib/lib/nsl
+	make %{INSTALLROOT}/lib/lib/nsl
 		make nsl.req
-			prev nsl.c
-			exec - mkreq-maplib ${CC} : nsl : ${^} : nsl
+			makp nsl.c
+			exec - mkreq-maplib %{CC} : nsl : %{^} : nsl
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
 	note *
 	note * what was sco smoking
 	note * almost all of gethost* are in -lnsl except gethostbyname which
 	note * is in -lsocket which isn't needed to resolve socket() but seems
 	note * to do the -lnsl job
 	note *
-	make ${INSTALLROOT}/lib/lib/socket
+	make %{INSTALLROOT}/lib/lib/socket
 		make socket.req
-			prev socket.c
+			makp socket.c
 			prev nsl.c
-			exec - mkreq-maplib ${CC} : socket : ${^} : socket
+			exec - mkreq-maplib %{CC} : socket : %{^} : socket
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
 	note *
 	note * more substance abuse
@@ -159,26 +165,26 @@ make install virtual
 	note *
 	note * at least the -l* buck stops here
 	note *
-	make ${INSTALLROOT}/lib/lib/dbm
+	make %{INSTALLROOT}/lib/lib/dbm
 		make dbm.req
-			prev db.c
-			prev gdbm.c
-			prev gdbm1.c
-			prev gdbm2.c
-			exec - mkreq-maplib ${CC} : dbm : ${^} : db gdbm_compat gdbm ndbm dbm
+			makp db.c
+			makp gdbm.c
+			makp gdbm1.c
+			makp gdbm2.c
+			exec - mkreq-maplib %{CC} : dbm : %{^} : db gdbm_compat gdbm ndbm dbm
 			prev mkreq-maplib
 		done
-		exec - cp -f ${<} ${@}
+		exec - cp -f %{<} %{@}
 	done
 done install
 
 make test dontcare virtual
 	make test.iffe virtual
-		prev iffe.tst
+		makp iffe.tst
 		exec - regress iffe.tst iffe
 	done
 	make test.mamake virtual
-		prev mamake.tst
+		makp mamake.tst
 		exec - : testing non-libast mamake at $PWD/mamake :
 		exec - regress mamake.tst mamake
 	done