[X86] RegCall - Handling long double arguments

The change is part of RegCall calling convention support for LLVM.
Long double (f80) requires special treatment as the first f80 parameter is saved in FP0 (floating point stack).
This review present the change and the corresponding tests.

Differential Revision: https://reviews.llvm.org/D26151


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287485 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed