[Bug libstdc++/69413] [6 Regression] r232327 prevents libstdc++ working after upgrading glibc to 2.23

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69413

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
GCC 6 will now work if it is built against glibc <= 2.22 and then glibc is
upgraded to >= 2.23

Using recent glibc 2.22 snapshots from git still requires rebuilding libstdc++.

Specifically, if you build GCC against glibc before
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d9b965fa56350d6eea9f7f438a0714c7ffbb183f
and then update glibc to a snapshot of 2.22 from git master after that commit,
libstdc++ will not work. In that case glibc still reports itself as 2.22 and
libstdc++ won't detect that the isinf and isnan declarations are gone, so must
be reconfigured and rebuilt against the new glibc headers.

When glibc releases 2.23 it weill be possible to upgrade to that without
rebuilding libstdc++, because the version bump will tell libstdc++ the
functions are gone.