mruby/mruby — pull request #2554 by dyama (2014-08-22 08:14:23+00:00)
Title: Fix the undefined function call for MSVC 2012 or older

Fix the undefined function call "copysign()" to "_copysign()" for MSVC 2012 or older.
MSVC provides C99 compatible name "copysign()" by 2013 or later.