Switch to gcc 4.6.3

[GoogleCodeExporter]

For 7400, 7450, G5,
-ftree-vectorize

For G5,
-mcpu=G5 -mno-powerpc64
and remove the stupid kludge we are using currently for 32-bit compiles.

These options are a little risky, so let's test them thoroughly.

Original issue reported on code.google.com by classi...@floodgap.com on 5 Apr 2011 at 10:44

• Blocking: Profile-guided optimization #6, [meta] Judgment Day #173, atexit handlers crash C++ runtime #169