cygwin: posix_spawn_file_actions_add[f]chdir[_np]

(backport <#4387>)
(cherry picked from commit e46d0c7)

Author: Berrysoft

libc-test/semver/cygwin.txt

@@ -734,8 +734,12 @@ posix_fadvise
 posix_fallocate
 posix_madvise
 posix_spawn
+posix_spawn_file_actions_addchdir
+posix_spawn_file_actions_addchdir_np
 posix_spawn_file_actions_addclose
 posix_spawn_file_actions_adddup2
+posix_spawn_file_actions_addfchdir
+posix_spawn_file_actions_addfchdir_np
 posix_spawn_file_actions_addopen
 posix_spawn_file_actions_destroy
 posix_spawn_file_actions_init

src/unix/cygwin/mod.rs

@@ -2479,6 +2479,22 @@ extern "C" {
         fd: c_int,
         newfd: c_int,
     ) -> c_int;
+    pub fn posix_spawn_file_actions_addchdir(
+        actions: *mut crate::posix_spawn_file_actions_t,
+        path: *const c_char,
+    ) -> c_int;
+    pub fn posix_spawn_file_actions_addfchdir(
+        actions: *mut crate::posix_spawn_file_actions_t,
+        fd: c_int,
+    ) -> c_int;
+    pub fn posix_spawn_file_actions_addchdir_np(
+        actions: *mut crate::posix_spawn_file_actions_t,
+        path: *const c_char,
+    ) -> c_int;
+    pub fn posix_spawn_file_actions_addfchdir_np(
+        actions: *mut crate::posix_spawn_file_actions_t,
+        fd: c_int,
+    ) -> c_int;
 
     pub fn forkpty(
         amaster: *mut c_int,