[rfc] Skip non-default multilib and libstdc++-v3 debug builds in bootstrap builds

[Richard Biener]

On Mon, Nov 30, 2015 at 12:34 AM, Matthias Klose <doko@ubuntu.com> wrote:
> The attached patch avoids building the non-default multilib and libstdc++-v3
> debug builds in bootstrap builds during bootstrap builds, resulting in some
> speedup for bootstrap builds for targets with multilibs enabled.  On
> x86_64-linux-gnu with 64/32/x32 multilibs enabled and the libstdc++ debug
> build enabled the bootstrap with -j8 takes 34:10 without, and with the patch
> 26:55, making the build ~20% faster (standard languages plus go enabled).
> It's faster because it avoids the rather sequential libcc/libstdc++/libgomp
> configury during stage1 and stage2.  The gain by not building the libstdc++
> debug library is not that measurable, the config is copied, there is no
> separate configure run.  Is relying on stage_current/stage_final the correct
> approach?  Should that be enabled using a configure option, or by default?

I think the more natural way would be to bootstrap the host libstdc++ and
only build the target libstdc++ for all multilibs.

Richard.

> Matthias
>