ucontext_t is missing on i686-unknown-freebsd

[jbeich]

wasmer-vm and wasmtime-runtime need ucontext_t + mcontext_t for PC and some other registers. Downstream (in ports/) this affects lapce, replibyte veloren, zellij on i386. For example,

error[E0412]: cannot find type `ucontext_t` in crate `libc`
   --> cargo-crates/wasmer-vm-2.3.0/src/trap/traphandlers.rs:219:57
    |
219 |             let ucontext = &mut *(context as *mut libc::ucontext_t);
    |                                                         ^^^^^^^^^^ not found in `libc`

error[E0412]: cannot find type `ucontext_t` in crate `libc`
   --> cargo-crates/wasmer-vm-2.3.0/src/trap/traphandlers.rs:259:45
    |
259 |         unsafe fn get_pc_sp(context: &libc::ucontext_t) -> (usize, usize) {
    |                                             ^^^^^^^^^^ not found in `libc`

error[E0412]: cannot find type `ucontext_t` in crate `libc`
   --> cargo-crates/wasmer-vm-2.3.0/src/trap/traphandlers.rs:314:54
    |
314 |         unsafe fn update_context(context: &mut libc::ucontext_t, regs: TrapHandlerRegs) {
    |                                                      ^^^^^^^^^^ not found in `libc`

Sorry, I can't provide a synthetic example.

[JohnTitor]

Note that it's usual that the crate doesn't have something, i.e. it's not a bug. Please use an API request template next time.