[LVI] Infer local facts from unary expressions

As pointed out by John Regehr over in http://reviews.llvm.org/D19485, LVI was being incredibly stupid about applying its transfer rules. Rather than gathering local facts from the expression itself, it was simply giving up entirely if one of the inputs was overdefined. This greatly impacts the precision of the overall analysis and makes it far more fragile as well.

This patch implements only the unary operation case. Once this is in, I'll implement the same for the binary operations.

Differential Revision: http://reviews.llvm.org/D19492

llvm-svn: 267609