Lex: Use the correct types for MS integer suffixes

Something went wrong with r211426, it is an older version of this code
and should not have been committed.  It was reverted with r211434.

Original commit message:
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