Merge branch 'break-in-conf' of https://github.com/dearblue/mruby into dearblue-break-in-conf

lib/mruby/build.rb

@@ -131,7 +131,12 @@ module MRuby
       end
 
       MRuby::Build.current = current
+      begin
         current.instance_eval(&block)
+      rescue Exception => err
+        raise
+      ensure
+        unless err
           if current.libmruby_enabled? && !current.mrbcfile_external?
             if current.presym_enabled?
               current.create_mrbc_build if current.host? || current.gems["mruby-bin-mrbc"]
@@ -141,6 +146,8 @@ module MRuby
           end
           current.presym = Presym.new(current) if current.presym_enabled?
         end
+      end
+    end
 
     def libmruby_enabled?
       @enable_libmruby