Include static prof data when collecting loop BBs

Summary:
If the programmer adds static profile data to a branch---i.e. uses
"__builtin_expect()" or similar---then we should honor it. Otherwise,
"__builtin_expect()" is ignored in crucial situations. So we trust that
the programmer knows what they're doing until proven wrong.

Subscribers: hiraditya, JDevlieghere, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74809