[phobos] linux.mak + osx.mak = GNUMakefile

[Walter Bright]

Andrei Alexandrescu wrote:
> Hey folks,
>
>
> I was building Phobos on OSX when I ran into a makefile bug that I'd 
> fixed in linux.mak. It was still present in osx.mak. I noticed the 
> files are virtually identical, so why not merge them?
>
> Since the one thing that linux.mak and osx.mak have in common is the 
> fact that they're understood by gnu make (as opposed to win32.mak 
> which is used by Walter's own make utility), I'm thinking the new 
> makefile should be called GNUMakefile. That name is actually 
> understood by gmake which means no more -f.
>
> I'm operating this change and will check in soon, please let me know 
> if you foresee any issues.
>

I prefer to keep them separate because:

1. It's very simple for the user to tell which makefile is for what 
system. With win32.mak and GNUmakefile it's wtf?
2. While they may be the same now, in the future they may be fairly 
different.
3. I like to drive make with my own makefile which then sets some macros 
and calls -flinux.mak, which would make it difficult to have a makefile 
that is the default name
4. It's *not* a burden to have two makefiles for different platforms. I 
think it's convenient and self-documenting to have a 1:1 correspondence 
between platforms and makefiles.
5. I like being able to futz with one without risk of breaking all the 
other platforms that I didn't test it on.
6. I find differences in gnu make from system to system, for example, 
FreeBSD has a much more primitive implementation on it.