libc: Add missing header for memset

Silence compiler warning by adding the missing string.h header
to include memset prototype.
Do some code tidy-up removing commented out libc_hidden_proto macros
in the meanwhile.

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

libc/signal/sigblock.c

@@ -19,8 +19,6 @@
 #define __UCLIBC_HIDE_DEPRECATED__
 #include <errno.h>
 #include <signal.h>
-#include <string.h>
-
 
 #include "sigset-cvt-mask.h"
 

libc/signal/sigpause.c

@@ -25,7 +25,6 @@
 #include <stddef.h>		/* For NULL.  */
 #include <string.h>
 
-
 #include "sigset-cvt-mask.h"
 
 /* Set the mask of blocked signals to MASK,

libc/signal/sigset-cvt-mask.h

@@ -19,6 +19,8 @@
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */
 
+#include <string.h>
+
 static __inline__ void __attribute__ ((unused))
 sigset_set_old_mask (sigset_t *set, int mask)
 {

libc/signal/sigsetmask.c

@@ -19,8 +19,6 @@
 #define __UCLIBC_HIDE_DEPRECATED__
 #include <errno.h>
 #include <signal.h>
-#include <string.h>
-
 
 #include "sigset-cvt-mask.h"