w32:spawn: Support pipe I/O for GPGRT_PROCESS_DETACHED.
* src/spawn-w32.c (struct gpgrt_spawn_actions): Add detached field. (spawn_detached): Merge into ... (_gpgrt_process_spawn): ... here, supporting pipe I/O. (_gpgrt_process_release): Handle detached process. (_gpgrt_process_wait_list): Likewise.
For old Windows, pipe I/O and NUL stdio are not supported for
a process with GPGRT_PROCESS_DETACHED. Creation of a process
can be done, but the process has INVALID HANDLE for stdio.
- GnuPG-bug-id: T7716
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>