[Patch draft] Fix libstdc++/8610

[Paolo Carlini]

Andreas Jaeger wrote:

>Are we compiling with -D_GNU_SOURCE ?  I think we do - and therefore
>it works in libstdc++.  If _GNU_SOURCE is set, we do not eed the
>LARGEFILE64_SOURCE.  But the latter might be needed for other
>platforms.
>
Indeed, we are. Thanks for your enlightening observation.
If, instead, I do:

paolo:~> g++ -U_GNU_SOURCE no-proto.cc
no-proto.cc: In function `int main()':
no-proto.cc:5: error: `lseek64' undeclared (first use this function)
no-proto.cc:5: error: (Each undeclared identifier is reported only once 
for each function it appears in.)

However, I'm not sure to understand what you mean by "other platforms":
I mean, libstdc++-v3 only comes with the corresponding g++, cannot be
used stand alone.

Another (reassurring) data point: you cannot actually use v3 with
-U_GNU_SOURCE: *many* things break well before lseek64 ;)

Paolo.