expose ppoll in default feature profile

the ppoll function has been accepted as a future part of the standard
as the outcome of Austin Group tracker issue 1263. at some point it
should be exposed unconditionally, but for now, expose it in the
default feature profile.

include/poll.h

@@ -36,7 +36,7 @@ struct pollfd {
 
 int poll (struct pollfd *, nfds_t, int);
 
-#ifdef _GNU_SOURCE
+#ifdef _BSD_SOURCE
 #define __NEED_time_t
 #define __NEED_struct_timespec
 #define __NEED_sigset_t
@@ -45,7 +45,7 @@ int ppoll(struct pollfd *, nfds_t, const struct timespec *, const sigset_t *);
 #endif
 
 #if _REDIR_TIME64
-#ifdef _GNU_SOURCE
+#ifdef _BSD_SOURCE
 __REDIR(ppoll, __ppoll_time64);
 #endif
 #endif

src/select/ppoll.c

@@ -1,4 +1,4 @@
-#define _GNU_SOURCE
+#define _BSD_SOURCE
 #include <poll.h>
 #include <signal.h>
 #include <errno.h>