unbound @1.9.2: fails to build in trace mode

[satraul (Satryaji Aulia)]

I have expat installed in both my prefixes /opt/local/ and /opt/macports-test/. Installing unbound on /opt/macports-test/ with tracemode fails because it tries to access expat.h in /opt/local/

:info:configure Command failed:  cd "/opt/macports-test/var/macports/build/_Users_satraul_git_macports-ports_net_unbound/unbound/work/unbound-1.9.2" && ./configure --prefix=/opt/macports-test --with-pidfile=/opt/macports-test/var/run/unbound/unbound.pid --with-ssl=/opt/macports-test --with-rootkey-file=/opt/macports-test/etc/unbound/root.key 
:info:configure Exit code: 1
:error:configure Failed to configure unbound, consult /opt/macports-test/var/macports/build/_Users_satraul_git_macports-ports_net_unbound/unbound/work/unbound-1.9.2/config.log
:warn:configure The following existing files were hidden from the build system by trace mode:
:msg:configure   /opt/local/include/expat.h
:msg:configure   /opt/macports-test/bin/ar
:msg:configure   /opt/macports-test/bin/bison

[jmroot (Joshua Root)]

The config.log may be helpful to see as well.

[neverpanic (Clemens Lang)]

​https://github.com/macports/macports-ports/pull/5006

[neverpanic (Clemens Lang)]

In e4a3accc807a08ffc588657e49f196bea0a4d8bc/macports-ports (master):

unbound: Fix build in non-default prefix

Unbound needs to be told where to look for libexpat, because it will
otherwise always attempt to use it from /opt/local.

Closes: #58815