I just discovered that t/silent-custom can fail if any parent of the build directory matches the "[012]\.h" regex. Specifically, the 'grep '[012]\.h' output && exit 1' command triggers a test failure.
(If you're wondering, one of my CI build-boxes just happened to kick off a build in a '/var/tmp/.build.automake_1.16.1-0.hzA5PJ' tmpdir.) Maybe refine this regex to " sub/[012]\.h"?
