bump LLVM version
Merge pull request #56 from regehr/bump-llvm

bump LLVM version
Apply UB constraints only on the relevant Phi branches

This patch fixes the unsoundness issue #13.
Add souper-check tool

This tool is based on souperweb-backend.cpp, but it's
intended to be run from the command line.
Merge pull request #60 from rsas/souper-check2

Add souper-check tool