fix SGC

Merge to 5.1.2

src/racket/sgc/sgc.c

@@ -2108,9 +2108,11 @@ void GC_dump(void)
   FPRINTF(STDERR, "End Map\n");
 }
 
-intptr_t GC_get_memory_use()
+long GC_get_memory_use()
 {
-  return mem_real_use;
+  /* returns a `long' instead of `intptr_t' for compatibility
+     with the Boehm GC */
+  return (long)mem_real_use;
 }
 
 void GC_end_stubborn_change(void *p)

src/racket/sgc/sgc.h

@@ -34,7 +34,7 @@ SGC_EXTERN void *GC_base(void *);
 
 SGC_EXTERN void GC_dump(void);
 
-SGC_EXTERN intptr_t GC_get_memory_use();
+SGC_EXTERN long GC_get_memory_use();
 
 SGC_EXTERN void GC_end_stubborn_change(void *);