Merge #70: build: Remove -Qunused-arguments workaround for clang + ccache

98f87c5 build: Remove `-Qunused-arguments` workaround for clang + ccache (Hennadii Stepanov)

Pull request description:

  The issue was addressed in [ccache 3.2](https://bugzilla.samba.org/show_bug.cgi?id=8118), and from a look at most major distros, it's only Debian Jessie that has a version of ccache older than that ([3.1](https://repology.org/project/ccache/versions)).

  Therefore I think it's acceptable to drop this workaround, and re-enable warnings for unused driver arguments (when compiling using Clang and ccache).

  This description quoted from bitcoin/bitcoin#18535.

ACKs for top commit:
  sipa:
    ACK 98f87c5

Tree-SHA512: 1ade0de95ca6f3465b35702d3e964f4fc5c070f00ce163d8cbd4ab52362ac56e0e9d412a0c1ddfd808714bad46cd79084da16966d387a4ebc776ceaf8a5bce88

Author: sipa

configure.ac

@@ -124,9 +124,6 @@ if test "x$use_ccache" != "xno"; then
   fi
   AC_MSG_RESULT($use_ccache)
 fi
-if test "x$use_ccache" = "xyes"; then
-    AX_CHECK_COMPILE_FLAG([-Qunused-arguments],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Qunused-arguments"],,[[$CXXFLAG_WERROR]])
-fi
 
 VERIFY_DEFINES=-DMINISKETCH_VERIFY
 RELEASE_DEFINES=