Previously code generation for Word32Neg (implemented as Word32Xor
with -1) was somewhat adhoc and not complete. Now it's uniform
and supports the full range of operand2's.

TEST=cctest/test-instruction-selector-arm,cctest/test-run-machops
R=titzer@chromium.org

Review URL: https://codereview.chromium.org/434923002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22789 ce2b1a6d-e550-0410-aec6-3dcde31c8c00