Define LLVM_NOEXCEPT with MSVC 14 CTP 3 or newer

We have to use _MSC_FULL_VER here as CTP 2 and earlier didn't define
noexcept to my knowledge.

Fixes build error in lib/Support/Error.cpp when inheriting from
std::error_category, which has a noexcept virtual method.

llvm-svn: 221013