configure.ac: set minimum GLIB version to 2.68

This fixes clang++ compilation as explained here:
  https://gitlab.gnome.org/GNOME/glib/-/issues/3193#note_1935964

It also introduces a lot of glib deprecated warnings

Signed-off-by: Balazs Scheidler <balazs.scheidler@axoflow.com>

CMakeLists.txt

@@ -229,7 +229,7 @@ find_package(BISON 3.7.6 REQUIRED)
 string(REGEX MATCH "^([0-9]+)\\.([0-9]+)\\..*$" _dummy "${BISON_VERSION}")
 
 set(GLIB_COMPILE_DEFINITIONS
-  GLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_32
+  GLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_68
 )
 find_package(GLIB 2.32.0 REQUIRED COMPONENTS gmodule gthread)
 

configure.ac

@@ -1025,8 +1025,6 @@ if test "$linking_mode" != "dynamic"; then
 	LIBS=$old_LIBS
 fi
 
-GLIB_CFLAGS="${GLIB_CFLAGS} -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_32"
-
 old_CPPFLAGS=$CPPFLAGS
 CPPFLAGS="$GLIB_CFLAGS"
 old_LDFLAGS=$LDFLAGS
@@ -1039,6 +1037,16 @@ AC_CHECK_FUNCS(g_list_copy_deep \
   g_canonicalize_filename)
 LIBS=$old_LIBS
 
+if "$HAVE_G_MEMDUP2" = "1"; then
+    dnl only set MIN_REQUIRED to 2.68 if we know that we are at least on that version.
+    dnl On CentOS7/SLES12 we don't have recent enough glib but with compat
+    dnl wrappers we can compile. Bad news is that if we don't set to 2_68 at least,
+    dnl we can't compile on new platforms with clang. Best of both worlds.
+    GLIB_CFLAGS="${GLIB_CFLAGS} -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_68"
+else
+    GLIB_CFLAGS="${GLIB_CFLAGS} -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_32"
+fi
+
 AC_CACHE_CHECK(sanity checking Glib headers,
                blb_cv_glib_sane,
 [AC_TRY_RUN([