[RFC] libstdc++: Make --enable-libstdcxx-backtrace=auto default to yes

[Jonathan Wakely]

On Fri, 1 Sept 2023 at 12:16, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> On Wed, 23 Aug 2023 at 17:03, Jonathan Wakely via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > Any objections to this? It's a C++23 feture, so should be enabled by
> > default.
>
> I've pushed this to trunk, so let's see what breaks!

This modules header broke on aarch64, of course:
FAIL: g++.dg/modules/xtreme-header_b.C -std=c++2b (test for excess errors)

>
>
> >
> > -- >8 --
> >
> > This causes libstdc++_libbacktrace.a to be built by default. This might
> > fail on some targets, in which case we can make the 'auto' choice expand
> > to either 'yes' or 'no' depending on the target.
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * acinclude.m4 (GLIBCXX_ENABLE_BACKTRACE): Default to yes.
> >         * configure: Regenerate.
> > ---
> >  libstdc++-v3/acinclude.m4 | 2 +-
> >  libstdc++-v3/configure    | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
> > index b25378eaace..50c808c6b2d 100644
> > --- a/libstdc++-v3/acinclude.m4
> > +++ b/libstdc++-v3/acinclude.m4
> > @@ -5481,7 +5481,7 @@ BACKTRACE_CPPFLAGS="$BACKTRACE_CPPFLAGS -DBACKTRACE_ELF_SIZE=$elfsize"
> >
> >    AC_MSG_CHECKING([whether to build libbacktrace support])
> >    if test "$enable_libstdcxx_backtrace" = "auto"; then
> > -    enable_libstdcxx_backtrace=no
> > +    enable_libstdcxx_backtrace=yes
> >    fi
> >    AC_MSG_RESULT($enable_libstdcxx_backtrace)
> >    if test "$enable_libstdcxx_backtrace" = "yes"; then
> >