Fix mcore libgloss port for c99/gcc-14

Missing headers and prototypes, much like other ports.

libgloss/mcore/kill.c

@@ -14,6 +14,8 @@
  */
 #include "glue.h"
 
+#include <unistd.h>
+
 /*
  * kill -- go out via exit...
  */

libgloss/mcore/putnum.c

@@ -14,6 +14,8 @@
  */
 #include "glue.h"
 
+extern void print (char *ptr);
+
 /*
  * putnum -- print a 32 bit number in hex
  */

libgloss/mcore/raise.c

@@ -14,6 +14,9 @@
  */
 #include "glue.h"
 
+extern int _kill (int, int);
+extern int _getpid (void);
+
 int
 _raise (int sig)
 {

libgloss/mcore/sbrk.c

@@ -16,6 +16,8 @@
 #include <sys/stat.h>
 #include "glue.h"
 
+extern int _write (int, char *, int);
+
 caddr_t
 _sbrk (size_t incr)
 {