fix: add pthread_spin_* definitions for the BSDs in std.c

* each BSD has a different one

lib/std/c.zig

@@ -7900,6 +7900,14 @@ pub const Stat = switch (native_os) {
 
 pub const pthread_spinlock_t = switch (native_os) {
     .openbsd => openbsd.pthread_spinlock_t,
+    .freebsd => extern struct {
+        inner: ?*anyopaque = null,
+    },
+    .netbsd => extern struct {
+        pts_magic: c_uint,
+        spin: pthread_spin_t,
+        pts_flags: c_int,
+    },
     .windows => isize,
     else => c_int,
 };