Summary:
Add basic functionality to support call lowering for X86.
Currently only supports functions which return void and take zero arguments.
Inspired by commit 286573.
Reviewers: ab, qcolombet, t.p.northover
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D26593
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286935 91177308-0d34-0410-b5e6-96231b3b80d8