Change libX11 variables to not conflict with AC_PATH_XTRA

The variable X_LIBS from AC_PATH_XTRA contains only the -L searchdir
parameter and not the -lX11 to link to Xlib. Use X11 prefixed build vars
for linking with Xlib to avoid the conflict.

Signed-off-by: Dan Nicholson <dbn.lists@gmail.com>
(cherry picked from commit e725ef171b)

src/gallium/state_trackers/glx/xlib/Makefile

@@ -6,7 +6,7 @@ LIBNAME = xlib
 LIBRARY_INCLUDES = \
 	-I$(TOP)/include \
 	-I$(TOP)/src/mesa \
-	$(X_CFLAGS)
+	$(X11_CFLAGS)
 
 C_SOURCES = \
 	glx_api.c \

src/gallium/winsys/xlib/Makefile

@@ -21,7 +21,7 @@ INCLUDE_DIRS = \
 	-I$(TOP)/src/gallium/drivers \
 	-I$(TOP)/src/gallium/state_trackers/glx/xlib \
 	-I$(TOP)/src/gallium/auxiliary \
-	$(X_CFLAGS)
+	$(X11_CFLAGS)
 
 DEFINES += \
 	-DGALLIUM_SOFTPIPE