[gentoo-releng] Setting --autounmask=n for autobuilds

[Ben Kohler]

Hi guys,

I'd like to propose adding --autounmask=n to EMERGE_DEFAULT_OPTS, at
least for nightheron builds but preferably everywhere.  Due to a known
portage bug [1], when a keyword or USE change is required by some
package, the chain of deps shown in the autounmask output cannot be
trusted.  It will very often blame the completely wrong package for
the unmask.

Since the autobuild process cannot make real use of autounmask anyway,
I propose that we turn it off.  The main downside I see, is that for
complex changes requiring several new package.* entries,
--autounmask=n will cause it to stop after only the first one is
printed.

But I think this will be worth it.  It will really help us quickly get
to the bottom of failures like this [2] and this [3].  BTW does anyone
know where those s390 builds happen?

Thoughts?

[1] https://bugs.gentoo.org/419381
[2] https://archives.gentoo.org/gentoo-releng-autobuilds/message/6a1c4b6bdfba9bc204af3172beb2287a
[3] https://archives.gentoo.org/gentoo-releng-autobuilds/message/8689b65e9502fba1717714cbf9514bd4

-Ben