Subzero: Fix build warnings/errors under g++.

BUG= none
TEST= make -j32 -f Makefile.standalone CXX=g++ LLVM_EXTRA_WARNINGS="-Wno-unknown-pragmas -Wno-unused-parameter -Wno-comment -Wno-enum-compare -Wno-strict-aliasing" STDLIB_FLAGS=
(this command will compile but fail to link)

R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1452993002 .
4 files changed