LLVM’s `LLVM_TARGETS_TO_BUILD` build flag defauls to `all`, which contains
`AMDGPU` among others. [1] Changes in llvm [2] switched to explicitly listing
host and target platforms, excluding the AMDGPU target, which is required
for Mesa to build.
[1]: db50b6fe39/CMakeLists.txt (L286-L302)
[2]: https://github.com/NixOS/nixpkgs/pull/52031
Since years I'm not maintaining anything of the list below other
than some updates when I needed them for some reason. Other people
is doing that maintenance on my behalf so I better take me out but
for very few packages. Finally!
Previously we only set these when using musl.
See https://github.com/NixOS/nixpkgs/pull/42452#discussion_r197618464
Same should be done for changes in #42452,
I'll add a follow-up commit doing so in the PR containing this
or wherever makes sense-- depending on how review/merging of that goes.
Sending similar changes for LLVM 4 to master, as suggested.
Build compiler-rt separate from llvm and clang, and just add as an extra
library in the wrapper.
(cherry picked from commit 16da44b5c115fe58048d7ba8aa597ed1598ea090)
