Your perl was built with a gcc that understands -Wdeclaration-after-statement. Yours doesn't. The following are the solution in increasing order or reliability:

• Hack it so it works (perhaps using ExtUtils::FakeConfig).
• Switch to a compatible compiler (perhaps by upgrading your gcc).
• Build a perl for your own use (perhaps using App::perlbrew, although it's easy to do from scratch too).