Add warning for C89-style variable declarations
make mruby build directory customizable
move declaration to the top of the block; ref #1727
Fix unused function warning when readline enabled (mirb)
support custom build_dir in CrossBuild
Merge pull request #1728 from kyab/fix_unused_error_mirb

Fix unused function warning when readline enabled (mirb)
Merge pull request #1729 from take-cheeze/customizable_build_dir

Make mruby build directory customizable.
Merge pull request #1727 from bggd/patch-2

Add warning for C89-style variable declarations