Include invoke'd functions for recursive extract

Summary: When recursively extracting a function from a bit code file, include functions mentioned in InvokeInst as well as CallInst

Reviewers: loladiro, espindola, volkan

Reviewed By: loladiro

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60231

llvm-svn: 357735