toolchain/44046: Parallel MKDEBUG builds randomly fail installing libraries

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         44046
>Category:       toolchain
>Synopsis:       Parallel MKDEBUG builds randomly fail installing libraries
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 05 14:40:00 +0000 2010
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current (multiple versions)
>Organization:
>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

Debug builds of NetBSD-current/i386, as in

  build.sh -j 6 -V MKDEBUG=YES -V COPTS=-g release

randomly fail about half the time, even though building from the same
source without the MKDEBUG and COPTS consistently succeeds.  The
failures all seem to involve an attempt to install a shared library
that has not yet been built, but the library involved is a different
one each time.  I'm cross-building from a Linux host, but I doubt that
matters.

The last 1000 lines of a representative build log can be found at

  http://www.gson.org/netbsd/bugs/lib-install/build.log

I suspect the problem appeared with bsd.lib.mk revision 1.307:

  date: 2010/04/27 14:32:14;  author: lukem;  state: Exp;  lines: +26 -3
  Support MKDEBUG for shared libraries.

because all the failures I have seen so far have been with sources
dated after that commit.

>How-To-Repeat:

Do a number of -current builds as described above, preferably on a
multi-CPU machine.  Watch some of them fail.

>Fix: