include string.h in strcpy.c to fix implicit declaration warnings

hanekawa/string/strcpy.c

@@ -15,6 +15,8 @@
  *  You should have received a copy of the GNU General Public License
  *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
+ 
+ #include <string.h>
 
 char *strcpy(char *restrict dest, const char *src) {
     stpcpy(dest, src);