Define GFX_XINERAMA_LIBS before it's used since EXTRA_DSO_LDOPTS gets evaluated immediately sometimes.

Bug #183894

gfx/src/gtk/Makefile.in

@@ -135,6 +135,10 @@ endif
 
 include $(topsrcdir)/config/rules.mk
 
+ifdef MOZ_ENABLE_XINERAMA
+GFX_XINERAMA_LIBS += $(MOZ_XINERAMA_LIBS)
+endif
+
 ifdef MOZ_ENABLE_GTK
 EXTRA_DSO_LDOPTS += \
 		$(LIBS_DIR) \
@@ -160,10 +164,6 @@ EXTRA_DSO_LDOPTS += $(MOZ_GTK_LDFLAGS) $(MOZ_XFT_LIBS) $(MOZ_GTK2_LIBS)
 CXXFLAGS	+= $(MOZ_GTK_CFLAGS) $(MOZ_GTK2_CFLAGS)
 CFLAGS		+= $(MOZ_GTK_CFLAGS) $(MOZ_GTK2_CFLAGS)
 
-ifdef MOZ_ENABLE_XINERAMA
-GFX_XINERAMA_LIBS += $(MOZ_XINERAMA_LIBS)
-endif
-
 ifeq ($(OS_ARCH), Linux)
 DEFINES         += -D_BSD_SOURCE
 endif