Cleanup mrb_str_resize().

make mrb_str_new_cstr DRY

Using str_new eliminates duplicated codes in mrb_str_new_cstr.

Fix compile warning for abort() when MRB_GC_STRESS is defined

fix typo: Tus -> Tue.

Fix and refactor crossbuild target config

Improve Test Infrastructure (Part 2)

Remove extra separator in compile command

Change seperator to separator