hp2ps/Utilities.c: add extern parameter types for malloc and realloc for C23

Fix build with gcc-15 which defaults to C23 standard (-std=gnu23)
Fixes #25662
```
utils/hp2ps/Utilities.c:6:14: error:
     warning: conflicting types for built-in function ‘malloc’; expected ‘void *(long unsigned int)’ [-Wbuiltin-declaration-mismatch]
        6 | extern void* malloc();
          |              ^~~~~~
  |
6 | extern void* malloc();
  |              ^
utils/hp2ps/Utilities.c:5:1: error:
     note: ‘malloc’ is declared in header ‘<stdlib.h>’
        4 | #include "Error.h"
      +++ |+#include <stdlib.h>
        5 | 
  |
5 | 
  | ^
utils/hp2ps/Utilities.c: In function ‘xmalloc’:
utils/hp2ps/Utilities.c:80:17: error:
     error: too many arguments to function ‘malloc’; expected 0, have 1
       80 |     r = (void*) malloc(n);
          |                 ^~~~~~ ~
   |
80 |     r = (void*) malloc(n);
   |                 ^
utils/hp2ps/Utilities.c:6:14: error:
     note: declared here
        6 | extern void* malloc();
          |              ^~~~~~
  |
6 | extern void* malloc();
  |              ^
utils/hp2ps/Utilities.c: In function ‘xrealloc’:
utils/hp2ps/Utilities.c:92:18: error:
     warning: conflicting types for built-in function ‘realloc’; expected ‘void *(void *, long unsigned int)’ [-Wbuiltin-declaration-mismatch]
       92 |     extern void *realloc();
          |                  ^~~~~~~
   |
92 |     extern void *realloc();
   |                  ^
utils/hp2ps/Utilities.c:92:18: error:
     note: ‘realloc’ is declared in header ‘<stdlib.h>’
   |
92 |     extern void *realloc();
   |                  ^
utils/hp2ps/Utilities.c:94:9: error:
     error: too many arguments to function ‘realloc’; expected 0, have 2
       94 |     r = realloc(p, n);
          |         ^~~~~~~ ~
   |
94 |     r = realloc(p, n);
   |         ^
utils/hp2ps/Utilities.c:92:18: error:
     note: declared here
       92 |     extern void *realloc();
          |                  ^~~~~~~
   |
92 |     extern void *realloc();
   |                  ^
```

utils/hp2ps/Utilities.c

@@ -3,7 +3,7 @@
 #include <string.h>
 #include "Error.h"
 
-extern void* malloc();
+extern void* malloc(long unsigned int);
 
 char*
 Basename(char *name)
@@ -89,7 +89,7 @@ void *
 xrealloc(void *p, size_t n)
 {
     void *r;
-    extern void *realloc();
+    extern void *realloc(void *, long unsigned int);
 
     r = realloc(p, n);
     if (!r) {