Add -Wno-pessimizing-move to Clang flags

Upstream clang has a new diagnostic '-Wpessimizing-move' that warns when
a std::move call prevents copy elision.  The warning (which turns into
an error with -Werror) is triggered for
  art/runtime/base/variant_map.h:261

Add -Wno-pessimizing-move to ART build rules until this warning can be
safely handled.

Change-Id: I7aff68abb6c44a5d64170b0d959c9537b89b5e16
1 file changed