JDK 9 RFR of JDK-8039865: Add fallthrough lint warning to build of jdk repository

[Joe Darcy]

Hello,

There are a relatively small number of "fallthrough" lint warnings in 
the sources of the JDK 9 jdk repo. Once those warnings are cleared 
(JDK-8039501), the fallthough lint option should be added to the build:

diff -r f1cc18a769e5 make/Setup.gmk
--- a/make/Setup.gmk    Tue Apr 08 17:36:13 2014 +0200
+++ b/make/Setup.gmk    Wed Apr 09 18:41:21 2014 -0700
@@ -27,7 +27,7 @@

  # To build with all warnings enabled, do the following:
  # make JAVAC_WARNINGS="-Xlint:all -Xmaxwarns 10000"
-JAVAC_WARNINGS := 
-Xlint:-unchecked,-deprecation,-overrides,auxiliaryclass,cast,classfile,dep-ann,divzero,empty,overloads,serial,static,try,varargs 
-Werror
+JAVAC_WARNINGS := 
-Xlint:-unchecked,-deprecation,-overrides,auxiliaryclass,cast,classfile,dep-ann,divzero,empty,fallthrough,overloads,serial,static,try,varargs 
-Werror

  # Any java code executed during a JDK build to build other parts of 
the JDK must be g
  # executed by the bootstrap JDK (probably with -Xbootclasspath/p: ) 
and for this

Thanks,

-Joe