CritBit: Be a little more friendly to MS cpp implementations.

src/post_modules/CritBit/tree_source.H

+#ifndef CB_GC_RECURSE_KEY
+# define CB_GC_RECURSE_KEY(X)
+#endif
+#ifndef CB_GC_CHECK_KEY
+# define CB_GC_CHECK_KEY(X)
+#endif
+
     INIT {
 	THIS->tree.root = NULL;
 	THIS->encode_fun = find_identifier
@@ -671,9 +678,7 @@ range_do_clone:
 	if (!node) return;
 	WALK_FORWARD(node, {
 	    if (CB_HAS_VALUE(_)) {
-#ifdef CB_GC_CHECK_KEY
 		CB_GC_CHECK_KEY(_->key);
-#endif
 		debug_gc_check_svalues(&_->value, 1,  " as a CritBit node value");
 	    }
 	});
@@ -684,9 +689,7 @@ range_do_clone:
 	if (!node) return;
 	WALK_FORWARD(node, {
 	    if (CB_HAS_VALUE(_)) {
-#ifdef CB_GC_RECURSE_KEY
 		CB_GC_RECURSE_KEY(_->key);
-#endif
 		gc_recurse_svalues(&_->value, 1);
 	    }
 	});