[InstCombine] MakeAnd/Or/Xor handling to reuse previous APInt computations

When checking if we should return a constant, we create some temporary APInts to see if we know all bits. But the exact computations we do are needed in several other locations in the same code.

This patch moves them to named temporaries so we can reuse them.

Ideally we'd write directly to KnownZero/One, but we currently seem to only write those variables after all the simplifications checks and I didn't want to change that with this patch.

Differential Revision: https://reviews.llvm.org/D32094

llvm-svn: 300376