Add support for Ananas platform

Ananas is a home-brew operating system, mainly for amd64 machines. After
using GCC for quite some time, it has switched to clang and never looked
back - yet, having to manually patch things is annoying, so it'd be much
nicer if this was in the official tree.

More information:

https://github.com/zhmu/ananas/
https://rink.nu/projects/ananas.html

Submitted by:	Rink Springer
Differential Revision:	https://reviews.llvm.org/D32936

llvm-svn: 306239