configure.in: deprecated-declarations

* configure.in: make deprecated declarations error.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44504 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
numeric.c: isfinite

* numeric.c (flo_is_finite_p): prefer C99 standard isfinite() than
  deprecated finite().

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44505 b2dd03c8-39d4-4d8f-98ff-823fe69b080e