crystal: 0.23.0 -> 0.23.1

Due to https://github.com/crystal-lang/crystal/issues/4719,
when building Crystal with LLVM 4 with debug infos from prebuilt binary (w/ LLVM 3.8) will always be failed.
The temporary solution is to build a LLVM 4 version without debug info,
then use it to build Crystal with debug info on LLVM 4.

This will cause building phrase going longer then normal.
We can remove this hack after Crystal fix the issue.