os/spawn: Add POSIX_SPAWN_ALLFLAG definition
This makes easy to check validation of flag.
#define POSIX_SPAWN_SETSCHEDULER (1 << 3) /* 1: Set task's scheduler policy */
#define POSIX_SPAWN_SETSIGDEF (1 << 4) /* 1: Set default signal actions */
#define POSIX_SPAWN_SETSIGMASK (1 << 5) /* 1: Set sigmask */
+#define POSIX_SPAWN_ALLFLAG (POSIX_SPAWN_RESETIDS | POSIX_SPAWN_SETPGROUP | POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER | POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK)
/****************************************************************************
* Type Definitions
