8011278: Allow using a system-installed giflib

Reviewed-by: andrew, prr

makefiles/CompileNativeLibraries.gmk

@@ -2387,18 +2387,23 @@ endif
 
 ifndef BUILD_HEADLESS_ONLY
 LIBSPLASHSCREEN_DIRS:=\
-	$(JDK_TOPDIR)/src/share/native/sun/awt/giflib \
 	$(JDK_TOPDIR)/src/share/native/sun/awt/image/jpeg \
 	$(JDK_TOPDIR)/src/share/native/sun/awt/libpng \
 	$(JDK_TOPDIR)/src/share/native/sun/awt/splashscreen
 
+ifeq ($(USE_EXTERNAL_LIBGIF),true)
+    GIFLIB_LDFLAGS := -lgif
+else
+    LIBSPLASHSCREEN_DIRS += $(JDK_TOPDIR)/src/share/native/sun/awt/giflib
+    GIFLIB_CFLAGS := -I$(JDK_TOPDIR)/src/share/native/sun/awt/giflib
+endif
+
 ifneq ($(OPENJDK_TARGET_OS), macosx)
     LIBSPLASHSCREEN_DIRS += $(JDK_TOPDIR)/src/$(OPENJDK_TARGET_OS_API_DIR)/native/sun/awt/splashscreen
 else
     LIBSPLASHSCREEN_DIRS += $(JDK_TOPDIR)/src/macosx/native/sun/awt/splashscreen
 endif
 
-
 LIBSPLASHSCREEN_CFLAGS:=-DSPLASHSCREEN -DPNG_NO_MMX_CODE \
 	$(foreach dir,$(LIBSPLASHSCREEN_DIRS),-I$(dir))
 
@@ -2450,11 +2455,11 @@ $(eval $(call SetupNativeCompilation,LIBSPLASHSCREEN,\
 		EXCLUDE_FILES:=imageioJPEG.c jpegdecoder.c pngtest.c,\
 		LANG:=C,\
 		OPTIMIZATION:=LOW, \
-		CFLAGS:=$(LIBSPLASHSCREEN_CFLAGS) $(CFLAGS_JDKLIB),\
+		CFLAGS:=$(LIBSPLASHSCREEN_CFLAGS) $(CFLAGS_JDKLIB) $(GIFLIB_CFLAGS),\
 		MAPFILE:=$(JDK_TOPDIR)/makefiles/mapfiles/libsplashscreen/mapfile-vers, \
 		LDFLAGS:=$(LDFLAGS_JDKLIB) \
 			 $(call SET_SHARED_LIBRARY_ORIGIN),\
-		LDFLAGS_SUFFIX:=$(LIBSPLASHSCREEN_LDFLAGS_SUFFIX) $(LIBZ),\
+		LDFLAGS_SUFFIX:=$(LIBSPLASHSCREEN_LDFLAGS_SUFFIX) $(LIBZ) $(GIFLIB_LDFLAGS),\
 		LDFLAGS_SUFFIX_solaris:=-lc,\
 		VERSIONINFO_RESOURCE:=$(JDK_TOPDIR)/src/windows/resource/version.rc,\
 		RC_FLAGS:=$(RC_FLAGS)\

src/share/native/sun/awt/splashscreen/splashscreen_gif.c

@@ -26,7 +26,7 @@
 #include "splashscreen_impl.h"
 #include "splashscreen_gfx.h"
 
-#include "../giflib/gif_lib.h"
+#include <gif_lib.h>
 
 #define GIF_TRANSPARENT     0x01
 #define GIF_USER_INPUT      0x02