bug#8881: config.h double inclusion

[Bruno Haible]

Alfred M. Szmidt wrote:
> >   > I think that autoconf should have the guard for double inclusion.
> >
> >   Autoconf does not need to provide a double-inclusion guard for
> >   config.h, because those packages that need it can get it through
> >   use of AH_TOP and AH_BOTTOM.
> 
> That is not a reason to not include such a guard.

Additionally,
  - Most often when a package has two config.h files, it needs to cumulate
    their definitions.
  - If Autoconf were to emit the double-inclusion guard, it would need an
    extra option to designate the C identifier. Too much complexity for
    something that is too much a special case.

Bruno
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