libs: spawn: Add forkaround for posix_spawn_file_actions_adddup2()

Summary:
- I noticed that adb shell failed when sh is spawned.
- Finally, I found that an error happened when executing dup2() action
  if the file descriptor has the O_CLOEXEC option.
- This commit fixes this issue by dropping the option in the API.

Impact:
- posix_spawn_file_actions_adddup2() only

Testing:
- adbd with sabre-6quad:netnsh (will be merged later)

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

libs/libc/spawn/lib_psfa_adddup2.c

@@ -28,6 +28,8 @@
 #include <spawn.h>
 #include <assert.h>
 #include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
 
 #include <nuttx/spawn.h>
 
@@ -64,6 +66,7 @@ int posix_spawn_file_actions_adddup2(
                          int fd1, int fd2)
 {
   FAR struct spawn_dup2_file_action_s *entry;
+  int flags;
 
   DEBUGASSERT(file_actions && fd1 >= 0 && fd2 >= 0);
 
@@ -83,6 +86,12 @@ int posix_spawn_file_actions_adddup2(
   entry->fd1    = fd1;
   entry->fd2    = fd2;
 
+  /* NOTE: Workaround to avoid an error when executing dup2 action */
+
+  flags = fcntl(fd1, F_GETFD);
+  flags &= ~FD_CLOEXEC;
+  fcntl(fd1, F_SETFD, flags);
+
   /* And add it to the file action list */
 
   add_file_action(file_actions,