Fix mcore libgloss port for c99/gcc-14

[Jeff Law]

[ So, there were more of these than I remembered :-) ]

Missing headers and prototypes, much like other ports.

Pushed to the trunk.

Jeff L.
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commit 73ba2873383da9028360052563945f37830f833a
Author: Jeff Law <jeffreyalaw@gmail.com>
Date:   Fri Dec 22 21:17:36 2023 -0700

    Fix mcore libgloss port for c99/gcc-14
    
    Missing headers and prototypes, much like other ports.

diff --git a/libgloss/mcore/kill.c b/libgloss/mcore/kill.c
index 833fe89d7..5cdd4d1fc 100644
--- a/libgloss/mcore/kill.c
+++ b/libgloss/mcore/kill.c
@@ -14,6 +14,8 @@
  */
 #include "glue.h"
 
+#include <unistd.h>
+
 /*
  * kill -- go out via exit...
  */
diff --git a/libgloss/mcore/putnum.c b/libgloss/mcore/putnum.c
index 10e298b95..f7e508b87 100644
--- a/libgloss/mcore/putnum.c
+++ b/libgloss/mcore/putnum.c
@@ -14,6 +14,8 @@
  */
 #include "glue.h"
 
+extern void print (char *ptr);
+
 /*
  * putnum -- print a 32 bit number in hex
  */
diff --git a/libgloss/mcore/raise.c b/libgloss/mcore/raise.c
index e39207792..6286d0eec 100644
--- a/libgloss/mcore/raise.c
+++ b/libgloss/mcore/raise.c
@@ -14,6 +14,9 @@
  */
 #include "glue.h"
 
+extern int _kill (int, int);
+extern int _getpid (void);
+
 int
 _raise (int sig)
 {
diff --git a/libgloss/mcore/sbrk.c b/libgloss/mcore/sbrk.c
index 844958984..1eb8047fc 100644
--- a/libgloss/mcore/sbrk.c
+++ b/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)
 {