Fix CANNOT_DUMP build on Darwin/macOS.

* src/conf_post.h (malloc, realloc, free) [DARWIN_OS && emacs &&
CANNOT_DUMP]: Don't define as unexec_malloc, etc.
* src/emacs.c (main): Don't call unexec_init_emacs_zone.

Author: Ken Raeburn

src/conf_post.h

@@ -94,7 +94,7 @@ typedef bool bool_bf;
 #endif
 
 #ifdef DARWIN_OS
-#ifdef emacs
+#if defined emacs && !defined CANNOT_DUMP
 #define malloc unexec_malloc
 #define realloc unexec_realloc
 #define free unexec_free

src/emacs.c

@@ -137,7 +137,7 @@ static
 bool might_dump;
 #endif
 
-#ifdef DARWIN_OS
+#if defined DARWIN_OS && !defined CANNOT_DUMP
 extern void unexec_init_emacs_zone (void);
 #endif
 
@@ -742,7 +742,7 @@ main (int argc, char **argv)
 #endif
 
 /* If using unexmacosx.c (set by s/darwin.h), we must do this. */
-#ifdef DARWIN_OS
+#if defined DARWIN_OS && !defined CANNOT_DUMP
   if (!initialized)
     unexec_init_emacs_zone ();
 #endif