Use cppflags to pass preprocessor options

.travis.yml

@@ -159,7 +159,7 @@ env:
     <<: *cron-only
     <<: *make-test-only
     env:
-      - BEFORE_INSTALL="sed vm_opts.h -e 's/OPT_SUPPORT_JOKE *0/OPT_SUPPORT_JOKE 1/' -i"
+      - cppflags=-DOPT_SUPPORT_JOKE
 
   - &CPDEBUG
     name: CPDEBUG
@@ -167,7 +167,7 @@ env:
     <<: *cron-only
     <<: *make-test-only
     env:
-      - DEFS="-DCPDEBUG"
+      - cppflags=-DCPDEBUG
 
   - &WITH_COROUTINE_UCONTEXT
     name: COROUTINE=ucontext

vm_opts.h

@@ -61,7 +61,9 @@
 #define OPT_STACK_CACHING            0
 
 /* misc */
+#ifndef OPT_SUPPORT_JOKE
 #define OPT_SUPPORT_JOKE             0
+#endif
 
 #ifndef VM_COLLECT_USAGE_DETAILS
 #define VM_COLLECT_USAGE_DETAILS     0