Lex: Use the correct types for MS integer suffixes

We didn't properly implement support for the sized integer suffixes.
Suffixes like i16 were essentially ignored instead of mapping them to
the appropriately sized integer type.

This fixes PR20008.

Differential Revision: http://reviews.llvm.org/D4132

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211426 91177308-0d34-0410-b5e6-96231b3b80d8