... in our test matrices.

`RUNALL_CROSSLIST` forms the cross product of all lines from above with all lines from below, and
from each pairing whose tag sets intersect produces a new line tagged with the intersection that
defines all variables defined on either line, with values that are the concatenation of the values
from `x` and `y`. Non-tagged lines are treated as if they are all tagged with the same value, and
`*` is the identity element for tag set intersection. For example:

```
	MEOW=A
X	MEOW=B
Y	MEOW=C
*	MEOW=D
RUNALL_CROSSLIST
	WOOF=1
X,Y	WOOF=2
X	WOOF=3
Y	MEOW=E WOOF=4
```
is equivalent to:
```
	MEOW=A WOOF=1
X	MEOW=B WOOF=2
X	MEOW=B WOOF=3
Y	MEOW=C WOOF=2
Y	MEOW="C E" WOOF=4
	MEOW=D WOOF=1
X,Y	MEOW=D WOOF=2
X	MEOW=D WOOF=3
Y	MEOW="D E" WOOF=4
```

[microsoftGH-4052](microsoft#4052) added `*` tags to all non-leaf lines
so they would properly combine with leaf configurations that have either an `ASAN` or empty tag.
There's a danger of "losing" `ASAN` configurations if we add a crosslist that inadvertently matches
untagged lines with `ASAN` lines. We decided that all lines should be tagged with either `ASAN` or
`*` to lessen the likelihood of such a mistake.