configure: Added option to disable Motif WM Hints support

The old behaviour was to expect the user to go modify manually a source
file which is not a great idea because that's typically the kind of things
in charge of the configure script.

As a side effect, we can now use an automake conditional to avoid compiling
the source file in charge of the feature when not used, instead of trying
to compile an empty-looking file.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

configure.ac

@@ -237,6 +237,7 @@ AX_PTHREAD
 dnl Tracking on what is detected for final status
 dnl =============================================
 unsupported=""
+supported_core=""
 supported_xext=""
 supported_gfx=""
 
@@ -286,6 +287,21 @@ AC_ARG_WITH(incs-from, AS_HELP_STRING([--with-incs-from], [pass compiler flags t
 	[inc_search_path="$withval $inc_search_path"])
 
 
+dnl Features Configuration
+dnl ======================
+AC_ARG_ENABLE([mwm-hints],
+    [AS_HELP_STRING([--disable-mwm-hints], [disable support for Motif WM hints @<:@default=enabled@:>@])],
+    [AS_CASE(["$enableval"],
+        [yes|no], [],
+        [AC_MSG_ERROR([bad value $enableval for --enable-mwm-hints])])],
+    [enable_mwm_hints="yes"])
+AS_IF([test "x$enable_mwm_hints" = "xno"],
+    [unsupported="$unsupported MWMHints"],
+    [AC_DEFINE([USE_MWM_HINTS], [1], [Defined when used did not request to disable Motif WM hints])
+     supported_core="$supported_core MWMHints"])
+AM_CONDITIONAL([USE_MWM_HINTS], [test "x$enable_mwm_hints" != "xno"])
+
+
 dnl Boehm GC
 dnl ========
 AC_ARG_ENABLE([boehm-gc],
@@ -887,6 +903,7 @@ echo "Installation path prefix            : $prefix"
 echo "Installation path for binaries      : $_bindir"
 echo "Installation path for libraries     : $libdir"
 echo "Installation path for WPrefs.app    : $wprefs_base_dir" | sed -e 's|\${prefix}|'"$prefix|"
+echo "Supported core features:            :$supported_core"
 echo "Supported X extensions:             :$supported_xext"
 echo "Supported graphic format libraries  :$supported_gfx"
 echo "Unsupported features                :$unsupported"