Refactor PGO function naming and MD5 hashing support out of ProfileData

Summary:
Move the function renaming logic into the Function class, and the
MD5Hash routine into the MD5 header.

This will enable these routines to be shared with ThinLTO, which
will be changed to store the MD5 hash instead of full function name
in the combined index for significant size reductions. And using the same
function naming for locals in the function index facilitates future
integration with indirect call value profiles.

Reviewers: davidxl

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D17006

llvm-svn: 260197