[IPCP] Don't crash due to arg count/type mismatch between caller/callee

Summary:
This patch avoids an assert in IPConstantPropagation when
there is a argument count/type mismatch between the caller and
the callee.

While this is actually UB on C-level (clang emits a warning),
the IR verifier seems to accept it. I'm not sure what other
frontends/languages might think about this, so simply bailing out
to avoid hitting an assert (in CallSiteBase<>::getArgOperand or
Value::doRAUW) seems like a simple solution.

The problem is exposed by the fact that AbstractCallSites will look
through a bitcast at the callee position of a call/invoke.

Reviewers: jdoerfert, reames, efriedma

Reviewed By: jdoerfert, efriedma

Subscribers: eli.friedman, efriedma, llvm-commits

Differential Revision: https://reviews.llvm.org/D57052

llvm-svn: 352469