Today's one is a parallel build system bug where `unbound` sometimes fails to build with `make -j16`. The gist of it is:
# somewhere in Makefile
parser.c parser.h: parser.y
$(YACC) -d -o parser.c parser.y
What's wrong with it?
The spoiler: https://github.com/NLnetLabs/unbound/pull/1167
`make --shuffle -j16` triggers it about 10% of the time.
