Support C++ in libtools.make and rewrite dependency handling.

- Change suffix of objects and depencency files to keep the original file
  suffix. This makes it easy to distinguish between C and C++ files when
  building and avoids implicit make rules trying to build in a way we don't
  want to.
- Implicitly handle dependencies instead of having an explicit rule. Simplifies
  things a bit.
- Support C++ files by adding an explicit rule for them. With keeping the
  original file suffixes this becomes quite simple.
  To use C++ files simply add them to SOURCES (or LIBSOURCES).

Change-Id: I22c56a6e153e281cfa675e91ad4a70fd18e2c43c
1 file changed