w32:spawn: Fix thread-unfriendly internal check.
* src/gpgrt-int.h (_gpgrt_windows_feature): New. * src/init.c (windows_specific_init): New. (real_init) [HAVE_W32_SYSTEM]: Call windows_specific_init. (_gpgrt_windows_feature): New. * src/spawn-w32.c (check_windows_version): Remove. (_gpgrt_process_spawn): Use _gpgrt_windows_feature.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>