Fix checksums GC_record_fault invocation on Darwin

* checksums.c [MPROTECT_VDB] (GC_record_fault): Define regardless of
DARWIN.
* include/private/gc_priv.h [CHECKSUMS && MPROTECT_VDB]
(GC_record_fault): Declare regardless of DARWIN.
* os_dep.c [MPROTECT_VDB && DARWIN && CHECKSUMS]
(catch_exception_raise): Call GC_record_fault() (if GC_mprotect_state
is GC_MP_NORMAL only).

checksums.c

@@ -36,7 +36,7 @@ STATIC word GC_faulted[NSUMS] = { 0 };
 
 STATIC size_t GC_n_faulted = 0;
 
-#if defined(MPROTECT_VDB) && !defined(DARWIN)
+#ifdef MPROTECT_VDB
   void GC_record_fault(struct hblk * h)
   {
     word page = (word)h & ~(word)(GC_page_size-1);

include/private/gc_priv.h

@@ -2793,7 +2793,7 @@ GC_EXTERN signed_word GC_bytes_found;
 #endif
 
 #ifdef CHECKSUMS
-# if defined(MPROTECT_VDB) && !defined(DARWIN)
+# ifdef MPROTECT_VDB
     void GC_record_fault(struct hblk * h);
 # endif
   void GC_check_dirty(void);

os_dep.c

@@ -5015,6 +5015,9 @@ catch_exception_raise(mach_port_t exception_port GC_ATTR_UNUSED,
     struct hblk * h = (struct hblk *)((word)addr & ~(word)(GC_page_size-1));
     size_t i;
 
+#   ifdef CHECKSUMS
+      GC_record_fault(h);
+#   endif
     UNPROTECT(h, GC_page_size);
     for (i = 0; i < divHBLKSZ(GC_page_size); i++) {
       word index = PHT_HASH(h+i);