Reverting r215966, r215965, r215964, r215963, r215960, r215959, r215958, and r215957 (these commits all rely on previous commits) due to build breakage. These commits cause failed assertions when testing Clang using MSVC 2013. The asserts are triggered from the std::equal call within ArrayRef::equals due to being passed invalid input (ArrayRef.begin() is returning a nullptr which is problematic).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215981 91177308-0d34-0410-b5e6-96231b3b80d8