sstephenson/ruby-build — pull request #478 by mrkn (2013-12-24 14:36:53+00:00)
Title: Set -Wno-error=shorten-64-to-32 only for Ruby >= 1.9.3 and use warnflags for it

Using warnflags is not overwrite CFLAGS. It allows us to specify optflags,
debugflags, and warnflags.