build: Retrieve X11 cflags and libraries

When using pkg-config to check for the x11 package compiler flags and
libraries we actually need to retrieve those values from the pc file.

This should also fix the issue with non-canonical installations of the
X11 headers and shared objects.

http://bugzilla.openedhand.com/show_bug.cgi?id=1966

configure.ac

@@ -459,6 +459,11 @@ AS_IF([test "x$CLUTTER_WINSYS" = "xglx" || test "x$CLUTTER_WINSYS" = "xeglx"],
         AS_IF([test "x$have_x11" = "xyes"],
               [
                 X11_PC_FILES="x11"
+
+                # we actually need to ask for CFLAGS and LIBS
+                X11_CFLAGS=`$PKG_CONFIG --cflags $X11_PC_FILES`
+                X11_LIBS=`$PKG_CONFIG --libs $X11_PC_FILES`
+
                 AC_MSG_RESULT([found])
               ],
               [