Add -Wno-unused-but-set-variable to the Dalvik project.

This is to meet long term goal that we don't suppress any warnings in
the global makefile.

BUG: 10495043
Change-Id: I1eece42a9f2c43b614cfbeb1397c8071fb3db04a
(cherry picked from commit 0c4625a4e1464544625723b013b3febb1cc9359e)