8196985: Disable new warnings from GCC 7.3 in jdk libraries

Reviewed-by: tbell, ihse
diff --git a/make/launcher/Launcher-jdk.pack.gmk b/make/launcher/Launcher-jdk.pack.gmk
index fed0ac8..af1fe13 100644
--- a/make/launcher/Launcher-jdk.pack.gmk
+++ b/make/launcher/Launcher-jdk.pack.gmk
@@ -82,7 +82,7 @@
     CFLAGS_linux := -fPIC, \
     CFLAGS_solaris := -KPIC, \
     CFLAGS_macosx := -fPIC, \
-    DISABLED_WARNINGS_gcc := unused-result, \
+    DISABLED_WARNINGS_gcc := unused-result implicit-fallthrough, \
     MAPFILE := $(UNPACK_MAPFILE),\
     LDFLAGS := $(UNPACKEXE_ZIPOBJS) \
         $(LDFLAGS_JDKEXE) $(LDFLAGS_CXX_JDK) \