Fixes "GC_BENCH" is not defined in extensions including zend_gc.h

Compilation warning encountered:

include/php/Zend/zend_gc.h:49:5: warning: "GC_BENCH" is not defined, evaluates to 0 [-Wundef]
   49 | #if GC_BENCH
      |     ^~~~~~~~

Author: patrickallaert

Zend/zend_gc.c

@@ -70,10 +70,6 @@
 #include "zend_API.h"
 #include "zend_fibers.h"
 
-#ifndef GC_BENCH
-# define GC_BENCH 0
-#endif
-
 #ifndef ZEND_GC_DEBUG
 # define ZEND_GC_DEBUG 0
 #endif

Zend/zend_gc.h

@@ -20,6 +20,10 @@
 #ifndef ZEND_GC_H
 #define ZEND_GC_H
 
+#ifndef GC_BENCH
+# define GC_BENCH 0
+#endif
+
 BEGIN_EXTERN_C()
 
 typedef struct _zend_gc_status {