Fix posix_spawn not being used on iOS and visionOS

`man posix_spawn` documents it to be able to return `ENOENT`, and there
should be nothing preventing this. Tested in the iOS simulator and on
Mac Catalyst.

Author: madsmtm

std/src/sys/pal/unix/process/process_unix.rs

@@ -420,13 +420,11 @@ impl Command {
     }
 
     #[cfg(not(any(
-        target_os = "macos",
-        target_os = "tvos",
-        target_os = "watchos",
         target_os = "freebsd",
         all(target_os = "linux", target_env = "gnu"),
         all(target_os = "linux", target_env = "musl"),
         target_os = "nto",
+        target_vendor = "apple",
     )))]
     fn posix_spawn(
         &mut self,
@@ -439,14 +437,11 @@ impl Command {
     // Only support platforms for which posix_spawn() can return ENOENT
     // directly.
     #[cfg(any(
-        target_os = "macos",
-        // FIXME: `target_os = "ios"`?
-        target_os = "tvos",
-        target_os = "watchos",
         target_os = "freebsd",
         all(target_os = "linux", target_env = "gnu"),
         all(target_os = "linux", target_env = "musl"),
         target_os = "nto",
+        target_vendor = "apple",
     ))]
     fn posix_spawn(
         &mut self,
@@ -530,7 +525,7 @@ impl Command {
         }
         let addchdir = match self.get_cwd() {
             Some(cwd) => {
-                if cfg!(any(target_os = "macos", target_os = "tvos", target_os = "watchos")) {
+                if cfg!(target_vendor = "apple") {
                     // There is a bug in macOS where a relative executable
                     // path like "../myprogram" will cause `posix_spawn` to
                     // successfully launch the program, but erroneously return