FreeBSD arm64/aarch64 support

#### Feature

Add FreeBSD support on arm64/aarch64

#### Implementation

Add to https://github.com/bytecodealliance/wasmtime/blob/main/crates/runtime/src/traphandlers/unix.rs
```
} else if #[cfg(all(target_os = "freebsd", target_arch = "aarch64"))] {
pc = context.uc_mcontext.mc_gpregs.gp_elr as usize;
sp = context.uc_mcontext.mc_gpregs.gp_sp as usize;
```
I take this code from https://github.com/wasmerio/wasmer/blob/dcfdea76999a/lib/vm/src/trap/traphandlers.rs#L302-L304 but don't know if some change needs to be made.

0.2.5 build log:
https://pkg-status.freebsd.org/ampere3/data/131arm64-default/b02e58aec16f/logs/lapce-0.2.5_1.log