Re: isnan function conflicts with C++ standard library declarations

["Martin Storsjö" <martin@martin.st>]

On Wed, 28 Aug 2019, Bruno Haible wrote:

>>>> This issue can crop up e.g. when trying to build gettext for mingw (which
>>>> has got the gnulib isnan function bundled, even if it isn't used).
>>>
>>> I'm regularly building gettext on mingw and haven't seen this issue. Therefore
>>> thanks again for the reproduction example.
>>
>> I ran into it while trying to build gettext with clang (with my pure-llvm
>> based toolchain, at https://github.com/mstorsjo/llvm-mingw in case you're
>> interested), so I presume there's something that goes different in gettext
>> with clang/lld compared to gcc
>
> Yes. It would make sense to compare the config.status file generated by an llvm
> build with those generated by a gcc build.

Just for the record, I believe the root cause is the fact that libc++'s 
stdlib.h (which is included before the normal C runtime's stdlib.h) 
includes math.h since this change: https://reviews.llvm.org/D60097

So math.h ends up included at a place where it isn't, when building with 
libstdc++, exposing the incompatibility between the gnulib math.h's isnan 
and C++, while other builds of the C++ code in gettext wouldn't include 
math.h at all.

// Martin