make warning: ?: No such file or directory.

On recent CURRENT, the source tree /usr/src seems to have issues on some of my
boxes and whenever I issue "make buildXXXX", the message:

make warning: �: No such file or directory.

pops up. "svn st" doesn't reveal anything wrong.

My locale settings are:

LANG=
LC_CTYPE="C"
LC_COLLATE="C"
LC_TIME="C"
LC_NUMERIC="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_ALL=

(just for the record). Those spooky non-printables are seen on xterm(s) of
various other systems (11.0, 11-STABLE, 12-CURRENT) when connecting to the
systems in question.

What is this?

Kind regards and thanks in advance,

oh