# The llvm a spell that says nothing about slots gets is slot 0 -- the
# system llvm, in /usr -- so 'cast llvm' is what it always was and
# every other spell's 'depends llvm' still means it.  The older majors
# are slots of their own, cast as llvm:21, llvm:20, llvm:16 and
# llvm:15, and install beside it under /opt/llvm<major>, which is where
# the spells the last three were made from wanted to go.
0 22 21 20 16 15

.