Use -DMMTK_WB_ASSERT_VO in CI

This will help detecting dangling pointers earlier.

Author: wks

.github/scripts/ci-build.sh

@@ -31,17 +31,27 @@ pushd $RUBY_PATH
 
     case $DEBUG_LEVEL in
         debug)
-            ../configure --with-mmtk-ruby=$BINDING_PATH --with-mmtk-ruby-debug --prefix=$RUBY_INSTALL_PATH --disable-install-doc cppflags='-g3 -O0 -DRUBY_DEBUG=1 -DRUBY_DEVEL -DUSE_RUBY_DEBUG_LOG=1'
+            ../configure \
+                --with-mmtk-ruby=$BINDING_PATH \
+                --with-mmtk-ruby-debug \
+                --prefix=$RUBY_INSTALL_PATH \
+                --disable-install-doc \
+                cppflags='-g3 -O0 -DRUBY_DEBUG=1 -DRUBY_DEVEL -DUSE_RUBY_DEBUG_LOG=1 -DMMTK_WB_ASSERT_VO'
             make miniruby -j $CI_JOBS
             ;;
 
         release)
-            ../configure --with-mmtk-ruby=$BINDING_PATH --prefix=$RUBY_INSTALL_PATH --disable-install-doc cppflags='-g3'
+            ../configure \
+                --with-mmtk-ruby=$BINDING_PATH \
+                --prefix=$RUBY_INSTALL_PATH \
+                --disable-install-doc cppflags='-g3 -DMMTK_WB_ASSERT_VO'
             make install -j $CI_JOBS
             ;;
 
         vanilla)
-            ../configure --prefix=$RUBY_INSTALL_PATH --disable-install-doc cppflags='-g3'
+            ../configure \
+                --prefix=$RUBY_INSTALL_PATH \
+                --disable-install-doc cppflags='-g3'
             make install -j $CI_JOBS
             ;;
         *)