core.sys.posix.spawn: Add OpenBSD bindings

Author: PetarKirov

src/core/sys/posix/spawn.d

@@ -28,6 +28,8 @@ https://github.com/opensource-apple/xnu (GitHub mirror)
 FreeBSD: https://github.com/freebsd/freebsd/blob/master/include/spawn.h
 
 NetBSD: https://github.com/NetBSD/src/blob/trunk/sys/sys/spawn.h
+
+OpenBSD: https://github.com/openbsd/src/blob/master/include/spawn.h
 */
 
 version (OSX) // macOS and iOS only as this API is prohibited on WatchOS and TVOS
@@ -282,5 +284,22 @@ else version (NetBSD)
         posix_spawn_file_actions_entry_t* fae;
     }
 }
+else version (OpenBSD)
+{
+    // Source: https://github.com/openbsd/src/blob/master/include/spawn.h
+    enum
+    {
+        POSIX_SPAWN_RESETIDS = 0x01,
+        POSIX_SPAWN_SETPGROUP = 0x02,
+        POSIX_SPAWN_SETSCHEDPARAM = 0x04,
+        POSIX_SPAWN_SETSCHEDULER = 0x08,
+        POSIX_SPAWN_SETSIGDEF = 0x10,
+        POSIX_SPAWN_SETSIGMASK = 0x20
+    }
+    alias posix_spawnattr_t = __posix_spawnattr*;
+    alias posix_spawn_file_actions_t = __posix_spawn_file_actions*;
+    struct __posix_spawnattr;
+    struct __posix_spawn_file_actions;
+}
 else
     static assert(0, "Unsupported OS");