Use GNU/Linux frame registration code for FreeBSD too

This change prevents a long hang when a program exits.

FreeBSD's `__deregister_frame` and `__register_frame` implementations
are ported from GCC, which is why we should be using the same frame
registration code for FreeBSD and GNU/Linux.

Link: https://github.com/freebsd/freebsd-src/blob/release/13.1.0/contrib/llvm-project/libunwind/src/UnwindLevel1-gcc-ext.c#L241-L299
Fixes: #3373

lib/compiler/src/engine/unwind/systemv.rs

@@ -60,7 +60,10 @@ impl UnwindRegistry {
 
     #[allow(clippy::cast_ptr_alignment)]
     unsafe fn register_frames(&mut self, eh_frame: &[u8]) {
-        if cfg!(all(target_os = "linux", target_env = "gnu")) {
+        if cfg!(any(
+            all(target_os = "linux", target_env = "gnu"),
+            target_os = "freebsd"
+        )) {
             // Registering an empty `eh_frame` (i.e. which
             // contains empty FDEs) cause problems on Linux when
             // deregistering it. We must avoid this