8057751: CompileNativeLibraries for custom build

Summary: Invoke CompileNativeLibraries in custom/closed build
Reviewed-by: dholmes

make/CompileNativeLibraries.gmk

@@ -87,6 +87,9 @@ include lib/Awt2dLibraries.gmk
 
 include lib/SoundLibraries.gmk
 
+# Include the corresponding custom file, if present. 
+-include $(CUSTOM_MAKE_DIR)/CompileNativeLibraries.gmk
+
 ##########################################################################################
 
 all: $(COPY_FILES) $(BUILD_LIBRARIES)