[block-freq] Add a method to loop info for returning all loop latches for a specific loop.

We already have a method for returning one loop latch but for some
reason no one has committed one for returning loop latches in the case
where there are multiple latches.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195410 91177308-0d34-0410-b5e6-96231b3b80d8
[block-freq] Update data in test case to be unsigned long long to fix mingw build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195411 91177308-0d34-0410-b5e6-96231b3b80d8