limit preserved significand length
Always include build_config.rb to compile dependency.

build_config.rb modifies `cc.defines` (eg. `DISABLE_GEMS`) so files depending on such flags should be rebuilt.

Ref. (Failing scenario): https://gist.github.com/cho45/9181191
add MRB_ prefix to STRINGIZE macro
Add target example for Intel Galileo board
Merge pull request #1735 from h2so5/limit-significand-length

limit preserved significand length
Merge pull request #1734 from kyab/add_galileo_config

Add target example for Intel Galileo board
Merge pull request #1733 from take-cheeze/mrb_stringize

add MRB_ prefix to STRINGIZE macro
Merge pull request #1732 from cho45/depend-build-config

Always include build_config.rb to compile dependency.