Add riscv64gc-unknown-freebsd target
I have had to patch libc and libstd to target FreeBSD 13.x ABI since riscv64 GENERIC does not enable COMPAT_*.
- Figure out why rustc crashes with SIGBUS while compiling the parse-zoneinfo crate
- Do a native build of lang/rust on riscv64. There is no cmake in the riscv64 package repository so I haven't tried it yet
- Try on real hardware (do not have any)
- Let other people look it over
- Upstream pull request: https://github.com/rust-lang/rust/pull/91284