Allow @ before identifer names. Recognize the i1, i8, i16, i32, i64 keywords
as type names corresponding to bool, ubyte, ushort, uint, and ulong
respectively. While these aren't LLVM 1.9 constructs, permitting the syntax
allows post-1.9 assembly files to be upgraded.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34023 91177308-0d34-0410-b5e6-96231b3b80d8