AsmParser: Verifier that the contents of a hex integer are hex

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223856 91177308-0d34-0410-b5e6-96231b3b80d8
Forgot to add test for r223856

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223857 91177308-0d34-0410-b5e6-96231b3b80d8