Haiku : execve not allowed if other pthreads have already been created

Signed-off-by: Sylvain78 <sylvain_kerjean@hotmail.com>

otherlibs/stdune/src/proc.ml

@@ -11,9 +11,7 @@ let restore_cwd_and_execve prog argv ~env =
   (* run at_exit before changing the working directory *)
   Stdlib.do_at_exit ();
   Sys.chdir (Path.External.to_string Path.External.initial_cwd);
-  let os_haiku = Sys.os_type == "BeOS" || (try ignore(Sys.getenv "BE_HOST_CPU");true with Not_found -> false)
-  in
-  if Sys.win32 || os_haiku  
+  if Sys.win32 || Platform.OS.value == Platform.OS.Haiku
   then (
     let pid = Unix.create_process_env prog argv env Unix.stdin Unix.stdout Unix.stderr in
     match snd (Unix.waitpid [] pid) with