files is empty. Sometimes the variable contains one or more spaces,
and testing against "" gave the wrong result, but applying the
:M* modifier discards the spaces. This should fix PR 45396.
* Instead of using "-" to ignore the exit status from the rm command,
use ||true. This should work around the bug in PR 45356, but that
bug is not fixed.
* Suppress the ${MKMSG} command with .if 0. People who build with
MAKEVERBOSE=1 don't want to see the message, and people who build
with MAKEVERBOSE=2 or higher will see the actual rm command. The
message may be useful for debugging this makefile itself, so it's
only disabled, not deleted.
