[sledge] Fix handling of bitcasts in call instr
[sledge] Fix handling of bitcasts in call instr

Summary:
Some call instructions in LLVM bitcast the function,
for example

`%call = call i32 (i64, ...) bitcast (i32 (...)* @__llair_alloc to i32 (i64, ...)*)(i64 %conv)`

This would cause sledge to crash in LLVM when build with assertions.

Reviewed By: jberdine

Differential Revision: D15779003

fbshipit-source-id: c273f92db

jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer