Fix for #31362 - ms_abi is implemented incorrectly for values >=16 bytes.

Fix for #31362 - ms_abi is implemented incorrectly for values >=16 bytes.

Summary:
This patch is a fix for following issue:
https://bugs.llvm.org/show_bug.cgi?id=31362 The problem was caused by front end
lowering C calling conventions without taking into account calling conventions
enforced by attribute. In this case win64cc was no correctly lowered on targets
other than Windows.

Reviewed By: rnk (Reid Kleckner)

Differential Revision: https://reviews.llvm.org/D43016

Author: belickim <mateusz.belicki@intel.com>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@324594 91177308-0d34-0410-b5e6-96231b3b80d8