[Bug other/67092] bootstrap failure in running genpreds, libstdc++ version mismatch

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67092

--- Comment #4 from vries at gcc dot gnu.org ---
(In reply to H.J. Lu from comment #3)
> Only build/genpreds in stage1 should be linked with libstdc++.so.6.

Why?

> Why are build/genpreds in stage2 and stage2 linked with libstdc++.so.6?

AFAICT, the -L bits here in src/Makefile.in:
...
POSTSTAGE1_CXX_EXPORT = \
        CXX='$(CXX)'; export CXX; \
        CXX_FOR_BUILD='$(CXX_FOR_BUILD)'; export CXX_FOR_BUILD;
@if target-libstdc++-v3-bootstrap
# Override the above if we're bootstrapping C++.
POSTSTAGE1_CXX_EXPORT = \
        CXX="$(STAGE_CC_WRAPPER) $$r/$(HOST_SUBDIR)/prev-gcc/xg++$(exeext) \
          -B$$r/$(HOST_SUBDIR)/prev-gcc/ -B$(build_tooldir)/bin/ -nostdinc++ \
          -B$$r/prev-$(TARGET_SUBDIR)/libstdc++-v3/src/.libs \
          -B$$r/prev-$(TARGET_SUBDIR)/libstdc++-v3/libsupc++/.libs \
          `if $(LEAN); then echo ' -isystem '; else echo ' -I';
fi`$$r/prev-$(TARGET_SUBDIR)/libstdc++-v3/include/$(TARGET_SUBDIR) \
          `if $(LEAN); then echo ' -isystem '; else echo ' -I';
fi`$$r/prev-$(TARGET_SUBDIR)/libstdc++-v3/include \
          `if $(LEAN); then echo ' -isystem '; else echo ' -I';
fi`$$s/libstdc++-v3/libsupc++ \
          -L$$r/prev-$(TARGET_SUBDIR)/libstdc++-v3/src/.libs \
          -L$$r/prev-$(TARGET_SUBDIR)/libstdc++-v3/libsupc++/.libs"; \
          export CXX; \
        CXX_FOR_BUILD="$$CXX"; export CXX_FOR_BUILD;
@endif target-libstdc++-v3-bootstrap
...