Problems building 11-stable/i386 with readonly /usr/src

[Kyle Evans]

On Sun, Feb 18, 2018 at 3:12 AM, Peter Jeremy <peter at rulingia.com> wrote:
> Sometime between r329122 and r329157, my 11-stable i386 box stopped
> being able to buildworld with a readonly /usr/src. I've been updating
> regularly but the problem still remains at r329450.  I don't have any
> problems building the same tree on amd64 or building head on i386 or
> amd64.  Does anyone have any ideas?
>
> Starting from an empty /usr/obj, the failure is:
> ...

This would have come in with the recent MFC of imp@'s rototilling. I
seem to recall some build system funkiness that put .OBJDIR inside the
src tree inconsistently before recent-ish changes in head. CC'ing
bdrewery@ and imp@ in hopes they have an idea of how to handle this in
stable/11. The offending ln invocation would be this one:
https://svnweb.freebsd.org/base/stable/11/stand/defs.mk?view=markup#l178