[Bug ada/81878] --disable-bootstrap --enable-languages=ada fails

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81878

--- Comment #18 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> all-gnattools: configure-gnattools
>         @: $(MAKE); $(unstage)
>         @r=`${PWD_COMMAND}`; export r; \
>         s=`cd $(srcdir); ${PWD_COMMAND}`; export s; \
>         $(HOST_EXPORTS)  \
>         (cd $(HOST_SUBDIR)/gnattools && \
>           $(MAKE) $(BASE_FLAGS_TO_PASS) $(EXTRA_HOST_FLAGS)
> $(STAGE1_FLAGS_TO_PASS)  \
>                 $(TARGET-gnattools))
> 
> so it builds for the host.  But when bootstrapping we want to build it
> similar to if it were a target library, that is, with the just built GCC.

Yes, that's what happens, i.e. the CXX passed to gnattools is CXX_FOR_TARGET.

> So,
> 
> host_modules= { module= gnattools; };
> 
> is technically not correct.  Not sure how it works during bootstrap, I'd have
> expected that the host compiler is used as well (gnattools is not bootstrapped).

This would simply break, because the gnattools really need to be bootstrapped
as they generally cannot be built by the host compiler.  Quite puzzling indeed.