Fix 'phpdbg --help' segfault on shutdown with USE_ZEND_ALLOC=0

This hack not only breaks the handling of custom allocators, but also
breaks if zend_alloc is compiled with USE_CUSTOM_MM.
This hack is just no good, if you want leak information then use ASAN.

Closes GH-18813.

Author: ndossche

NEWS

@@ -39,6 +39,9 @@ PHP                                                                        NEWS
   . Add missing filter cleanups on phar failure. (nielsdos)
   . Fixed bug GH-18642 (Signed integer overflow in ext/phar fseek). (nielsdos)
 
+- PHPDBG:
+  . Fix 'phpdbg --help' segfault on shutdown with USE_ZEND_ALLOC=0. (nielsdos)
+
 - PDO ODBC:
   . Fix memory leak if WideCharToMultiByte() fails. (nielsdos)
 

sapi/phpdbg/phpdbg.c

@@ -179,12 +179,6 @@ static PHP_MSHUTDOWN_FUNCTION(phpdbg) /* {{{ */
 		phpdbg_notice("Script ended normally");
 	}
 
-	/* hack to restore mm_heap->use_custom_heap in order to receive memory leak info */
-	if (use_mm_wrappers) {
-		/* ASSUMING that mm_heap->use_custom_heap is the first element of the struct ... */
-		*(int *) zend_mm_get_heap() = 0;
-	}
-
 	if (PHPDBG_G(buffer)) {
 		free(PHPDBG_G(buffer));
 		PHPDBG_G(buffer) = NULL;