build: configure return exit status from gyp

Previously, 'configure' would not return an exit status
if gyp blows up. This can be tested via:

    date >> node.gyp ; ./configure && echo A-OK

You will get "A-OK" even though gyp had failed.

PR-URL: https://github.com/joyent/node/pull/8856
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>