Enable 32/64-bit gyp switch on Linux

Linux defaults to 64, other platforms 32.  As of this change, only Mac and
Linux are affected by the skia_arch_width flag.  Next step is to make Win
work as well.
Review URL: https://codereview.appspot.com/6460066

git-svn-id: http://skia.googlecode.com/svn/trunk@5041 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed