configure: Automatically detect the default xorg-module-dir.

The module directory has changed to a per ABI folder in the xlibre-xserver.
Now the default value of `xorg-module-dir` will be detected from the `moduledir` variable in xorg-server.pc.

Signed-off-by: b-aaz <b-aazbsd.proton.me>

Makefile.am

@@ -18,6 +18,10 @@
 #  IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 #  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+# During distcheck, system locations (as provided by pkg-config) may
+# not be writable; provide instead relative locations.
+DISTCHECK_CONFIGURE_FLAGS = --with-xorg-module-dir='$${libdir}/xorg/modules'
+
 #Having problems passing through user flags as libtool complains
 #ACLOCAL_AMFLAGS = ${ACLOCAL_FLAGS} -I m4
 ACLOCAL_AMFLAGS = -I m4

configure.ac

@@ -303,11 +303,12 @@ AM_CONDITIONAL(BUILD_TOOLS, test "x$tools" != "xno")
 AM_CONDITIONAL(BUILD_TOOL_CURSOR, test "x$cursor" = "xyes")
 
 # Define a configure option for an alternate module directory
+PKG_PROG_PKG_CONFIG([0.25])
 AC_ARG_WITH(xorg-module-dir,
             AS_HELP_STRING([--with-xorg-module-dir=DIR],
-                           [Default xorg module directory [[default=$libdir/xorg/modules]]]),
+                           [Default xorg module directory]),
             [moduledir="$withval"],
-            [moduledir="$libdir/xorg/modules"])
+            [moduledir=`$PKG_CONFIG --variable=moduledir xorg-server`])
 
 AC_ARG_ENABLE(dri,
 	      AS_HELP_STRING([--disable-dri],