futimens: add missing local prototype

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
(cherry picked from commit d0a8b14169c6f01dadd07f6b4e14cc335a62f234)

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>

libc/sysdeps/linux/common/futimens.c

@@ -21,6 +21,7 @@ extern int utimensat (int __fd, __const char *__path,
 	int __flags) __THROW;
 libc_hidden_proto(utimensat)
 
+int futimens (int __fd, __const struct timespec __times[2]) __THROW;
 int futimens (int fd, __const struct timespec ts[2])
 {
 	return utimensat(fd, 0, ts, 0);