Add ms_abi and sysv_abi attribute handling.

Based on a patch by Benno Rice!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189644 91177308-0d34-0410-b5e6-96231b3b80d8
Simplify slightly.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189645 91177308-0d34-0410-b5e6-96231b3b80d8
Don't eagerly load all conversion operators when loading a class declaration
from a PCH/module.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189646 91177308-0d34-0410-b5e6-96231b3b80d8