Use cr1 for FPR->GPR conversion exceptions

[GoogleCodeExporter]

1. Move the mtfsb0 exception enable instructions to the trampoline from the 
square root routine.
2. Remove convertInt32ToDouble from branchConvertDoubleToInt32, mcrf cr1 to 
cr0, and branch on that directly. (This *should* work given the way the branch 
failure cases work.)

Not for stable, since this uses some instructions recently added for Ion.

Original issue reported on code.google.com by classi...@floodgap.com on 5 May 2013 at 8:54

• Blocking: Implement BaselineCompiler #224