llvm-profdata: Update to use the naive text format with function hash

This also uses line_iterator to simplify the parsing logic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204210 91177308-0d34-0410-b5e6-96231b3b80d8
llvm-profdata: Make "merge" into a subcommand.

We'll be adding a few more subcommands in the near future.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204211 91177308-0d34-0410-b5e6-96231b3b80d8