Fix m_Not and m_Neg to not match random ConstantInt's. Before

these would try hard to match constants by inverting the bits
and recursively matching.  There are two problems with this:
1) some patterns would match when we didn't want them to (theoretical)
2) this is insanely expensive to do, and most often pointless.

This was apparently useful in just 2 instcombine cases, which I
added code to handle explicitly.  This change speeds up 'opt'
time on 176.gcc by 1% and produces bitwise identical code.

llvm-svn: 123518