[Bug libfortran/87182] New: libbacktrace does not use GCC own zlib

[vigerske at math dot hu-berlin.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87182

            Bug ID: 87182
           Summary: libbacktrace does not use GCC own zlib
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libfortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vigerske at math dot hu-berlin.de
                CC: ibuclaw at gdcproject dot org
  Target Milestone: ---

The configure of libbacktrace checks for -lz without considering the build of
zlib in ../../libz (the one that GCC builds). That is, libbacktrace introduces
a dependency on the systems zlib in libgfortran even if --with-system-zlib has
not been set.

It seems that this was introduced with rev 253275:
https://gcc.gnu.org/viewcvs/gcc/trunk/libbacktrace/configure.ac?r1=253095&r2=253275
Rev 263320 does some cosmetic change
(https://gcc.gnu.org/viewcvs/gcc/trunk/libbacktrace/configure.ac?r1=256169&r2=263320),
but doesn't fix this issue (imho).