build: upgrade libtool macros.

	* configure.ac: here.
	* Makefile.am: Enable dependencies on libtool.

Author: akimd

Makefile.am

@@ -7,6 +7,9 @@
 
 ACLOCAL_AMFLAGS = -I build-aux/m4
 
+libtool: $(LIBTOOL_DEPS)
+	$(SHELL) ./config.status libtool
+
 # Sources to build library
 LIBSOURCES = jaricom.c jcapimin.c jcapistd.c jcarith.c jccoefct.c jccolor.c \
         jcdctmgr.c jchuff.c jcinit.c jcmainct.c jcmarker.c jcmaster.c \

configure.ac

@@ -269,9 +269,10 @@ int main() {
 AC_DEFINE([DONT_USE_B_MODE],[1],[Don't open files in binary mode.])],
 AC_MSG_RESULT(Assuming that it does.))
 
-# Configure libtool
-AC_LIBTOOL_WIN32_DLL
-AC_PROG_LIBTOOL
+# Configure libtool.
+LT_PREREQ([2.2.6])
+LT_INIT([win32-dll])
+AC_SUBST([LIBTOOL_DEPS])
 
 # The name of the library to build (not including the "lib" prefix).
 # Defaults to "jpeg", but can be changed to another name to avoid