configure.ac: Fix breakage caused by -Werror=unused-variable

[Daniel Santos]

On 09/08/2015 12:31 AM, Alexandre Julliard wrote:
> Daniel Santos <daniel.santos at pobox.com> writes:
>
>> On 09/07/2015 04:53 AM, Alexandre Julliard wrote:
>>> Daniel Santos <daniel.santos at pobox.com> writes:
>>>
>>>> When configuring with CFLAGS="-Wunused-variable -Werror", the configure
>>>> test for HAVE_PNG_SET_EXPAND_GRAY_1_2_4_TO_8 fails with unused variable.
>>> Running configure with -Werror is not a good idea. Is there a particular
>>> reason why you need this?
>>>
>> Not for configure in particular, but for the build I prefer to have
>> the highest level of warnings enabled (that won't produce spam) and
>> I've found -Werror a good way to make sure that none slip past me.
> It would be better to specify CFLAGS at make time. Making configure
> -Werror proof is not possible given the wide variety of environments it
> needs to support.
>
Ahh, so I see. I guess I didn't realize that you could do that! :)