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.
Review URL: http://codereview.chromium.org/174154

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2734 ce2b1a6d-e550-0410-aec6-3dcde31c8c00