gcc isn't present on BSD systems, instead check for 'cc'

[erikarn]

Hi! The autoconf script checks for 'gcc' being present, rather than 'cc' being present. This makes it not run out of the box on FreeBSD without hacking on things - we do have GCC ports, but since we support >1 GCC version being installed, they're named gcc.

The easy solution is to change configure.in to check for 'cc' instead of 'gcc'. If you could commit that then I'll be able to build this out of the box on FreeBSD!

Thanks!