* hookapi.cc (find_first_notloaded_dll): New function.

* hookapi.cc (find_first_notloaded_dll): New function.
* pinfo.cc (status_exit): New function.  Issue message when dll not found.  Use
find_first_notloaded_dll to find a nonexistent dll.
(pinfo::maybe_set_exit_code_from_windows): Call status_exit when exit code >=
0xc0000000UL.
* sigproc.cc (child_info::proc_retry): Return exit code when
STATUS_DLL_NOT_FOUND.
* spawn.cc (spawn_guts): Minor cleanup.
* syscalls.cc (close_all_files): Don't actually close stderr filehandle.  Just
make it noninheritable.
* winsup.h (find_first_notloaded_dll): Declare new function.
* ntdll.h: Add several missing NTSTATUS defines.