[LLVM-C] Improve Bindings to The Internalize Pass

Summary: Adds a binding to the internalize pass that allows the caller to pass a function pointer that acts as the visibility-preservation predicate.  Previously, one could only pass an unsigned value (not LLVMBool?) that directed the pass to consider "main" or not.

Reviewers: whitequark, deadalnix, harlanhaskins

Reviewed By: whitequark, harlanhaskins

Subscribers: kren1, hiraditya, llvm-commits, harlanhaskins

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62456

llvm-svn: 366777