[X86] Add support for elfiamcu triple

This adds support for the i?86-*-elfiamcu triple, which indicates the IAMCU psABI is used.

Differential Revision: http://reviews.llvm.org/D13977

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251222 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed