Allow dynamically shared library

Change-Id: I08c4019e28ca68abb1241370294ac4dd1303fe34
v8: Fix build in ISO C++ 11 mode

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>
libv8: set unused attribute for unused parameters

Summary:
On GCC 4.8+ we get excessive unused parameter warnings due to -Wunused-parameter.
Set __attribute__((unused)) for all unused parameters.

Test Plan:
Build libv8 with this patch and gcc 4.8, and enjoy a much cleaner log due to the lack of unused parameter
warnings.

Reviewers: randall.rushing, Mustaavalkosta, michyprima, rlasalle15, Roach, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D212