configure: use gcc and g++ as CC and CXX defaults
configure: use gcc and g++ as CC and CXX defaults

It matches what GYP's Makefile generator does and it should improve
compiler detection because cc and c++ are not always gcc and g++.

Fixes: https://github.com/iojs/io.js/issues/1173
PR-URL: https://github.com/iojs/io.js/pull/1174
Reviewed-By: Johan Bergström <3e38e5ce4283f06de4b83ad13af081abc5e16740@bergstroem.nu>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node