patch 9.0.1557: test failures for unreachable code

Problem:    Test failures for unreachable code.
Solution:   Add a test override to ignore unreachable code.
diff --git a/src/globals.h b/src/globals.h
index 3e8b753..69b4343 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1914,6 +1914,7 @@
 EXTERN long override_sysinfo_uptime INIT(= -1);
 EXTERN int  override_autoload INIT(= FALSE);
 EXTERN int  ml_get_alloc_lines INIT(= FALSE);
+EXTERN int  ignore_unreachable_code_for_testing INIT(= FALSE);
 
 EXTERN int  in_free_unref_items INIT(= FALSE);
 #endif