8196988: Resolve disabled warnings for libjimage

Fixed warnings related to implicit-fallthrough gcc option

Reviewed-by: psandoz, mchung

make/lib/CoreLibraries.gmk

@@ -195,7 +195,6 @@ $(eval $(call SetupJdkLibrary, BUILD_LIBJIMAGE, \
     OPTIMIZATION := LOW, \
     CFLAGS := $(CFLAGS_JDKLIB), \
     CXXFLAGS := $(CXXFLAGS_JDKLIB), \
-    DISABLED_WARNINGS_gcc := implicit-fallthrough, \
     CFLAGS_unix := -UDEBUG, \
     LDFLAGS := $(LDFLAGS_JDKLIB) $(LDFLAGS_CXX_JDK) \
         $(call SET_SHARED_LIBRARY_ORIGIN), \

src/java.base/share/native/libjimage/imageDecompressor.cpp

@@ -322,6 +322,7 @@ void SharedStringDecompressor::decompress_resource(u1* data,
             {
                 i++;
             }
+            /* fall through */
             default:
             {
                 *uncompressed_resource = tag;