Building ath9k_htc with LLVM

[jscott0]

This is a tracking bug for being able to build this firmware with LLVM. If you haven't met me before, I'm John, the Debian package maintainer for this firmware. LLVM support for Xtensa is being merged imminently. This is a great opportunity to add support for building with LLVM to enhance ath9k_htc's robustness.

Right now using Binutils and GCC requires applying patches to tailor the Xtensa target to that found in the hardware, which is gross. I love GCC, but think that for Xtensa LLVM may well prove superior. Note that I'm not yet familiar with LLVM, so I don't know how we will set up the target information.

This bug is a keeping place for all information that may help this effort. Perhaps someday someone will be able to put together a merge request from it.