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

["vogt at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

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

--- Comment #3 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
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?  The hack I tried earlier still does not work:

$ g++ -std=c++11 x.C -v \
  --sysroot ~/src/git/glibc/install \
  -idirafter ~/src/git/glibc/install/usr/include \
  -idirafter /usr/local/include \
  -idirafter /usr/include

...
ignoring nonexistent directory "~/src/git/glibc/install/usr/local/include"
ignoring nonexistent directory
"~/src/git/gcc/install/lib/gcc/s390x-ibm-linux-gnu/6.0.0/../../../../s390x-ibm-linux-gnu/include"
ignoring duplicate directory "~/src/git/glibc/install/usr/include"
#include "..." search starts here:
#include <...> search starts here:

~/src/git/gcc/install/lib/gcc/s390x-ibm-linux-gnu/6.0.0/../../../../include/c++/6.0.0

~/src/git/gcc/install/lib/gcc/s390x-ibm-linux-gnu/6.0.0/../../../../include/c++/6.0.0/s390x-ibm-linux-gnu

~/src/git/gcc/install/lib/gcc/s390x-ibm-linux-gnu/6.0.0/../../../../include/c++/6.0.0/backward
 ~/src/git/gcc/install/lib/gcc/s390x-ibm-linux-gnu/6.0.0/include
 ~/src/git/gcc/install/include
 ~/src/git/gcc/install/lib/gcc/s390x-ibm-linux-gnu/6.0.0/include-fixed
 ~/src/git/glibc/install/usr/include
 /usr/local/include
 /usr/include
End of search list.
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