Enable -fstrict-aliasing in the GYP build of V8 for the Mac in Release mode

Enable -fstrict-aliasing in the GYP build of V8 for the Mac in Release mode.
-fstrict-aliasing is enabled by mainline gcc at -O2 and higher, but in Apple
gcc, it must be enabled explicitly.  This results in a 1.5% improvement in V8
benchmark scores.

This also removes the -fno-exceptions and -fno-rtti settings from v8.gyp for
the Mac, and removes -fno-rtti from v8.gyp for Linux, because these settings
have become part of Chromium's common.gypi, included here, as of r23304 at the
latest.  The settings in v8.gyp have become redundant.

Committed: http://code.google.com/p/v8/source/detail?r=2734

[Kasper Lund, 2009-08-20 19:12:21]

LGTM.