Let PassBuilder Expose PassInstrumentationCallbacks
Summary:
This is an effort to allowing external libraries register their own pass instrumentation during their llvmGetPassPluginInfo() calls.
By exposing this through the added getPIC(), now a pass writer can do something like this:
```
extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK
llvmGetPassPluginInfo() {
return {
..,
[](llvm::PassBuilder &PB) {
PB.getPIC()->registerAfterPassCallback(move(f));
}
};
}
```
Reviewers: chandlerc, philip.pfaffe, fedor.sergeev
Reviewed By: fedor.sergeev
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71086