Adds commit '65ce2e56889' from https://git.llvm.org/git/llvm as
'third_party/llvm-7.0/llvm'

Commands:
git remote add llvm https://git.llvm.org/git/llvm.git
git subtree add --prefix third_party/llvm-7.0/llvm llvm release_70 --squash

Bug b/115344057

Change-Id: I981f7e2fc47639ca8a8998b188e837bc3f268de5