implicit declarations in acinclude.m4

[Niels Möller]

Vincent Lefevre <vincent at vinc17.net> writes:

> And this probably includes GCC with -Werror. For instance, I now test
> MPFR with:
>
>   CFLAGS="-O2 -Wall -Wold-style-declaration -Wold-style-definition
>   -Wmissing-parameter-type -Wmissing-prototypes -Wmissing-declarations
>   -Wmissing-field-initializers -Wno-error=unused-function -Werror"
>
> to make sure that we follow the rules and detect potential problems
> ASAP.

Makes sense for development, but I don't think we should encourage use
of -Wall -Werror by users. It's a bit too brittle (e.g., if gcc starts
to suggest redundant braces or parentheses in some new context, that
breaks the build). On the other hand, I think it would make sense to
enable more warning options by default, when compiling with gcc.

(And this is of course not an objection to fixing warnings for the
configure test programs).

Regards,
/Niels

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