Generate dependency files with Clang (issue 555300044 by jonas.hahnfeld@gmail.com)

[lemzwerg--- via Discussions on LilyPond development]

Good idea, thanks!  LGTM.

Apropos .lo files: We can remove STEPMAKE_LIBTOOL in `aclocal.m4` since
it isn't used.  I think this change would probably fit into this issue,
too.

https://codereview.appspot.com/555300044/