configure.in: use C99

* configure.in: ISO9899:1999 is necessary for strtoll() on FreeBSD
  10, (and may be possibly other platforms).

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44876 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: extra quotes

* configure.in: remove extra quotes in message.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44877 b2dd03c8-39d4-4d8f-98ff-823fe69b080e