v8: Fix build in ISO C++ 11 mode

Summary:
Fixes building with -std=gnu++11 - this is useful for compatibility
with future compilers (where gnu++11 will be the default mode) and
to make additional language features/optimizations (e.g. constexpr)
available.

Change-Id: Ica4a220675f700c1f63d36f46460ca12168bdeb3
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>

Test Plan: verified

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D129