Fails to build on i686-unknown-freebsd

[jbeich]

Describe the bug

ca6f83c accidentally used target_arch = "x86" in FreeBSD support.

$ rustc -vV
rustc 1.68.2 (9eb3afe9e 2023-03-27) (built from a source tarball)
binary: rustc
commit-hash: 9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0
commit-date: 2023-03-27
host: i686-unknown-freebsd
release: 1.68.2
LLVM version: 15.0.6

Steps to reproduce

$ cargo build --package wasmer-vm
[...]
error: Unsupported platform
   --> lib/vm/src/trap/traphandlers.rs:403:21
    |
403 |                     compile_error!("Unsupported platform");
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0609]: no field `mc_rip` on type `mcontext_t`
   --> lib/vm/src/trap/traphandlers.rs:261:46
    |
261 |                     pc = context.uc_mcontext.mc_rip as usize;
    |                                              ^^^^^^ help: a field with a similar name exists: `mc_eip`

error[E0609]: no field `mc_rsp` on type `mcontext_t`
   --> lib/vm/src/trap/traphandlers.rs:262:46
    |
262 |                     sp = context.uc_mcontext.mc_rsp as usize;
    |                                              ^^^^^^ help: a field with a similar name exists: `mc_esp`

Expected behavior

Builds fine

Actual behavior

Fails to build because mcontext_t is different.

Additional context

See also rust-lang/libc#3196