Running bitcode module verifier in CodeGen tests

Hi all,

I'm trying to add some validation to the bitcode module verifier in a
situation where I know there should be an offending test within the
clang CodeGen tests, but it does not fire. When I piped the output
through llvm-as + llvm-dis, the verifier did fire in the llvm-as
invocation. It sounds important for at least the CodeGen tests to
undergo bitcode module verification. Digging in, I found that the
Backend_Emit(BC,LL) modes do not honor the CodeGenOpts.VerifyModule
flag (I guess that's because they definitionally skip CodeGen?).
Perhaps they should honor that flag anyway?