Zig's build script has several race conditions preventing proper
concurrent builds from working. By using -j1 for now, finishing this
branch (concurrent zig builds) is untangled from the separate problem of
correcting concurrency issues with zig's own build script.
In other words, let's solve one problem at a time.
In particular, these two changes are relevant:
* zig cc: support -stack in addition to --stack for linker arg
- Fixes stack overflow when running zig2 on aarch64-macos.
* compiler_rt: avoid using weak aliases
- Fixes duplicate symbol when linking zig2 on aarch64-linux.
In the CI system, I copied the old tarball and then applied
05c21a26cb2d5daf06191bd996d0770192704b66 to its compiler_rt
implementation.
After this is verified we can drop this commit and regenerate the
tarballs from a master branch commit.
Override the cache directories because they won't actually help other CI
runs which will be testing alternate versions of zig, and ultimately
would just fill up space on the hard drive for no reason.
In practice we did see one of the CI servers fill up too many files
inside ~/.cache/zig, which caused certain file system operations to
start returning ENOSPC, despite the hard drive having plenty of space
left.
