[WIP] Fix HAVE_CONFIG_H -Wundef warnings.

[Paul Eggert]

On 05/02/2014 01:28 AM, Will Newton wrote:
> The
> gnulib versions of the files have in some cases switched to use
> #ifndef _LIBC instead of #if HAVE_CONFIG_H  but I haven't delved into
> why that is yet.

Some years ago gnulib changed, and it now assumes that <config.h> always 
exists.  We surround the include with "#ifndef _LIBC" only for files 
shared with glibc.  If glibc is also going to assume config.h exists, I 
suggest getting rid of the #if, and using "#include <config.h>" 
unconditionally; that's simplest.