configure.in: clang check
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40031 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: clang check
AC_USE_SYSTEM_EXTENSIONS. [Bug #8192]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40031 b2dd03c8-39d4-4d8f-98ff-823fe69b080e