RFC: deprecate sys/sysmacros.h inclusion from sys/types.h

[Roland McGrath]

> Hmm, good point.  The macro was for programs that *are* being broken
> because they didn't expect sys/types.h to define major/minor/makedev,
> and advising such programs to #undef those symbols is better advice,
> since that will work on *BSDs that still define them there.

Yes, that is harmless now and will be harmless in the future and does not
look like gratuitous cruft in the same way.

> >> +#ifdef __USE_EXTERN_INLINES
> >> +#define __SYSMACRO_IMPL(rtype, name, proto, expr) \
> >
> > An example of unintended preprocessor directives.
> 
> I assume you meant unindented.

Indeed.  Typing is hard.

> > Also, make all these macros __SYSMACROS_* instead of _SYSMACRO_* (so
> > the prefix matches the name of the header file).
> 
> I think singular is more appropriate because it expands to the
> implementation of *one* sysmacro.

"sysmacro" is not a thing.  "sysmacros" is the name of the file, and hence
the moniker for its private namespace.