Update Microsoft name mangling scheme for exception specifiers in the type system

Summary:
The msvc exception specifier for noexcept function types has changed
from the prior default of "Z" to "_E" if the function cannot throw when
compiling with /std:C++17.

Patch by Zachary Henkel!

Reviewers: zturner, rnk

Reviewed By: rnk

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D55685

llvm-svn: 349414