Optimize bitwise even/odd test (-x&1 -> x&1) to not use negation.

Summary: We know that -x & 1 is equivalent to x & 1, avoid using negation for testing if a negative integer is even or odd.

Reviewers: majnemer

Subscribers: junbuml, mssimpso, gberry, mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D12156

llvm-svn: 245569