Revamp error checking in the ms inline asm parser.

- Actually abort when an error occurred.
- Check that the frontend lookup worked when parsing length/size/type operators.

Tested by a clang test. PR18096.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196044 91177308-0d34-0410-b5e6-96231b3b80d8