depcomp: avoid trailing backslash in depfile for depmode=msvc7

depcomp: avoid trailing backslash in depfile for depmode=msvc7

When compiling a file without any dependencies (no #includes), the
msvc7 depmode (and consequently msvc7msys) generates a depfile
Makefile fragment with the last line ending with a backslash. This
is less robust than needed.

Fixes automake bug#14501.

* lib/depcomp (msvc7): Finish off the depfile Makefile fragment with
an empty line.
(scriptversion): Update.

Signed-off-by: Peter Rosin <peda@lysator.liu.se>