Rename C files to .c in GCC source

[Jonathan Wakely]

On 30 January 2015 at 22:24, Kevin Ingwersen (Ingwie Phoenix) wrote:
> Apple’s HFS is, on a default OS X install, case insensitive.

Which doesn't matter, see my previous reply.

> But .c++ is valid. .cxx sounds pretty straight forward to me, since people also use the $CXX variable.

We already use .C and .cc in GCC sources, so even if we needed to
change it, it would probably be better to use .cc for consistency
rather than add a third extension.