Bug 2336263

I'm experimentally rebuilding rawhide with the not-yet-released GCC 15 to see if anything breaks, and to help write the porting guide.  See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15

My test build with GCC 15 failed:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed/build/8476052/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed.checker/build/8477625/

Looking at the failure logs e.g.
https://download.copr.fedorainfracloud.org/results/dmalcolm/gcc-15-smoketest-3.failed/fedora-rawhide-x86_64/08476052-Singular/builder-live.log.gz

I see:

extra.cc: In function 'BOOLEAN jjEXTENDED_SYSTEM(leftv, leftv)':
extra.cc:3850:11: error: 'convSingPFlintP' was not declared in this scope
 3850 |           convSingPFlintP(fre,(poly)h->Data(),currRing); h=h->next;
      |           ^~~~~~~~~~~~~~~
extra.cc:3857:11: error: 'convSingNFlintN' was not declared in this scope
 3857 |           convSingNFlintN(center_re,(number)h->Data(),currRing->cf); h=h->next;
      |           ^~~~~~~~~~~~~~~
extra.cc:3892:27: error: 'convFlintNSingN' was not declared in this scope
 3892 |             ll->m[0].data=convFlintNSingN(re_part[i],currRing->cf);
      |                           ^~~~~~~~~~~~~~~

I've written some notes on C++ name lookup failures here:
  https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15#C++:_error_with_-Wtemplate-body
but the above error doesn't seem to be in a template, so this might well be a different problem.

Reproducible: Always