gallium: Respect user's CFLAGS for including X headers

This can break on systems that don't have a system X installation.

Signed-off-by: Dan Nicholson <dbn.lists@gmail.com>
(cherry picked from commit de4ee20578a79e024b0de83c40648112f42c994e)

Conflicts:

	src/gallium/winsys/xlib/Makefile
2 files changed