Rename C files to .c in GCC source

[Eli Zaretskii]

> From: DJ Delorie <dj@redhat.com>
> Cc: gcc@gcc.gnu.org, Jonny Grant <jg@jguk.org>
> Date: Fri, 30 Jan 2015 16:39:51 -0500
> 
> 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++).

Actually, Windows filesystems do allow '+' in file names.  (DOS
filesystems don't.)

But I agree that using it is not the best alternative, as the Windows
shell sometimes interprets '+' as a delimiter, so file names using
that character need to be quoted for safety.