Rename C files to .c in GCC source

[Kevin Ingwersen (Ingwie Phoenix)]

> Am 30.01.2015 um 22:39 schrieb DJ Delorie <dj@redhat.com>:
> 
> 
> pinskia@gmail.com writes:
>> No because they are c++ code so capital C is correct. 
> 
> However, we should avoid relying on case-sensitive file systems
> (Windows) and use .cc or .cxx for C++ files ("+" is not a valid file
> name character on Windows, so we can't use .c++).

Apple’s HFS is, on a default OS X install, case insensitive. But .c++ is valid. .cxx sounds pretty straight forward to me, since people also use the $CXX variable.