implement ffsl and ffsll functions

per the resolution of Austin Group issue #617, these are accepted for
XSI option in POSIX future and thus I'm treating them as standard
functions.

src/misc/ffsll.c

@@ -0,0 +1,7 @@
+#include <strings.h>
+#include "atomic.h"
+
+int ffsll(long long i)
+{
+	return i ? a_ctz_64(i)+1 : 0;
+}