configure: remove compiler detection

[seishun]

The GCC version is no longer relevant since only 4.8 and newer are supported. It's probably safe to assume clang on mac since V8 does so too.

[bnoordhuis]

Cheers Nikolai, landed in 0f3d7e6.

[saper]

I am working on getting sass/node-sass to build on FreeBSD and I'd like to use process.config.variables.clang to figure out if iojs was built on FreeBSD 8 or 9 (with gcc as the default compiler) or FreeBSD 10+ (with clang as the default). This is helpful in figuring out whether I need to ship binary binding that links to GNU libstdc++ or the one that works with clang libc++. More details:  sass/node-sass#733

I think this commit disabled process.config.variables.clang that is available in node 0.10.x and 0.12.x

[jbergstroem]

@saper I'm agree with @mgreter about binary releases not always being the best solution. A compiler check wouldn't necessary solve your problem since clang just as well can compile against libstdc++. I understand that you mostly care about FreeBSD for your binaries, but it'd still be a 90% solution. So, gunning for a 90% fix, I'd personally choose a different compromise (for instance only supporting FreeBSD 10+, leaving older users to compile their own).

[saper]

No problem, I will use it for node and will keep on guessing for iojs :)