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

[redi at gcc dot gnu.org]

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

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Dominik Vogt from comment #3)
> So, what is the proper way to compile
> 
>   -- snip --
>   #include <math.h>
>   -- snip --
> 
> using a current Gcc compiled with an old system Glibc so that the program
> uses a new (not installed) Glibc? 

You can't, that's not supported.

As I said, if you want to use glibc 2.22 headers from after the mentioned
commit, libstdc++ must be built with those same headers.

I thought this was fairly explicit:

(In reply to Jonathan Wakely from comment #2)
> 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.


As a quick hack you can bump the value of __GLIBC_MINOR__ in
~/src/git/glibc/install/usr/include/features.h to make it appear to be glibc
2.23, but obviously that isn't supported either.