configure.in: no -Wextra-token on gcc 3

* configure.in (warnflags): -Wextra-tokens is same as -Wextra and
  let -Wno- options ignored on gcc 3.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40131 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: gcc_major

* configure.in: use gcc_major value.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40132 b2dd03c8-39d4-4d8f-98ff-823fe69b080e