[V8] Fix stack alignment corruption for MinGW32 build

Contributed by Peter Varga <pvarga@inf.u-szeged.hu>

BUG=
TEST=cctest/test-assembler-ia32/StackAlignmentForSSE2,cctest/test-assembler-x64/StackAlignmentForSSE2,cctest/test-platform/StackAlignment
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/18300003

Patch from Peter Varga <pvarga@inf.u-szeged.hu>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15502 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

Change-Id: I17d6a6c53659da4cb3e5238395bd2ae6506d1201
Signed-off-by: Peter Varga <pvarga@inf.u-szeged.hu>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>