[build2] Problems running the `cxx20-modules-examples`

[Boris Kolpackov]

hjansen.iv via users <users at build2.org> writes:

> - using `g++` 2021-07-23 master snapshot for compiling the
>   `cxx20-modules-examples` suite.
>
> c++ ../../../../../../inst/gcc/20210723/include/c++/12.0.0/h{iosfwd}
> In file included from /home/hjansen/Software/inst/gcc/20210723/include/c++/12.0.0/bits/stl_iterator_base_types.h:71,
>                  from /home/hjansen/Software/inst/gcc/20210723/include/c++/12.0.0/bits/stl_algobase.h:65,
>                  from /home/hjansen/Software/inst/gcc/20210723/include/c++/12.0.0/bits/char_traits.h:39,
>                  from /home/hjansen/Software/inst/gcc/20210723/include/c++/12.0.0/string_view:42:
> /home/hjansen/Software/inst/gcc/20210723/include/c++/12.0.0/bits/iterator_concepts.h:34: internal compiler error: in set_filename, at cp/module.cc:19128

This appears to be a problem with GCC. The examples are know to mostly
work with the 11.1 release but it looks like things have gotten broken
since (which is not surprising since modules support is still in the
state of flux).

You can try to isolate the problem and report it to GCC but I wouldn't
bother -- there are so many open bugs in modules support that it's most
likely already reported. And if not, we can always report it closer to
the release.