[p0012] Implement ABI support for throwing a noexcept function pointer and

catching as non-noexcept

This implements the following proposal from cxx-abi-dev:

http://sourcerytools.com/pipermail/cxx-abi-dev/2016-October/002988.html

... which is necessary for complete support of http://wg21.link/p0012,
specifically throwing noexcept function and member function pointers and
catching them as non-noexcept pointers.

Differential Review: https://reviews.llvm.org/D26178

llvm-svn: 285867