* winsup.h: Define MAX_SID_LEN and new MAX_HOST_NAME.

* fork.cc (fork): Use above defines instead of numerical constants.
        * shared.cc (sec_user): Ditto.
        * shared.h (class pinfo): Ditto.
        * syscall.cc (seteuid): Ditto.
        * spawn.cc (_spawnve): Ditto. Eliminate conditional.
        (spawn_guts): Set child->uid = USHRT_MAX when user context will be
        changed in child process.
        * uinfo.cc (uinfo_init): Check for myself->uid instead of myself->psid
        to avoid reloading of /etc/passwd on process startup if ntsec is off.
        Use above defines instead of numerical constants.
        * security.cc: Move define for MAX_SID_LEN to winsup.h.

winsup/cygwin/winsup.h

@@ -67,6 +67,9 @@ extern int dynamically_loaded;
 #define DEFAULT_UID 500
 #define DEFAULT_GID 544
 
+#define MAX_SID_LEN 40
+#define MAX_HOST_NAME 256
+
 /* status bit manipulation */
 #define __ISSETF(what, x, prefix) \
   ((what)->status & prefix##_##x)