Makefile: Remove redirected target on fail

[okuoku]

(Copied from #349, sorry.)

When we use shell-redirection to generate target in Makefile, we have to remove failed output explicitly. Otherwise, we will get empty file as target even on failure case and next make invocation may fail on wrong place.

NOTE: Since I don't have OSX box right now, the patch haven't tested at all. (https://github.com/picrin-scheme/picrin/commit/d66ce6413018f31ac34c87b4c7a6b54daa72939b requires OSX to build the repository)

Alternatively, you may use .DELETE_ON_ERROR special target ( http://stackoverflow.com/questions/3587182 ) but it is gmake extension and I do not recommend doing so.

[nyuichi]

@okuoku

Thanks for the PR. I am currently working on reimplementation and replacement of the evaluator (VM) in picrin. After the work, we will have a tiny, robust CPS-based VM. What is on the master HEAD is all WIP stuff. I will fix the build script after the migration is done. I think it will be in this week.