tests/make: demonstrate interrupting make in compat mode

branches: 1.3.2;
make: handle .PHONY consitently on interrupt

JobDeleteTarget skips .PHONY targets
CompatDeleteTarget should do the same

This addresses https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=269663

make(1): fix test for interrupted command execution

In the first version of this test, I had completely misunderstood the
whole topic.

To test the interrupt, the make process has to be interrupted, not the
shell. This generates the correct message that the target is removed.

The filename for .PHONY targets is removed even though .PHONY targets
usually don't correspond to a file. The message is only printed if
there actually is a corresponding file. That's why this message does
not appear when interrupting "make clean".

Finally, since files get created and removed during a single run of
make, the file cache needs to be disabled. This is done by prefixing
the filenames with "././", see Dir_FindFile.

make(1): add test for interrupting a command