Perhaps there should be a comment explaining that you can’t write to $(srcdir). Or even a buildbot that does an out-of-tree build. Every now and then I seem to be defending against patches that want to change targets back to $(srcdir).

Also, Trent’s last change, revision 65b3c41052b6, does not seem to work. Apparently $abs_srcdir etc are only valid when substituted in a makefile, and are not valid in the configure script: <https://lists.gnu.org/archive/html/autoconf/2010-07/msg00021.html>. I will try to post a patch that addresses this to Issue 28066.