[Devel] revision of FT's make system

[Werner LEMBERG]

I've completely revised FreeType's make system to simplify its rules.
>From the ChangeLog:

        . In all makefiles `/' is used as the path separator.  The
          conversion to the real path separators is done as late as
          possible using $(subst ...).

        . $(HOSTSEP) no longer exists.  Now, $(SEP) gives the path
          separator for the operating system, and the new
          $(COMPILER_SEP) the path separator for the compiler tools.

        . $(BUILD) has been renamed to $(BUILD_DIR).  In general, all
          directory variables end with `_DIR'.  The variants ending in
          `_' (like `BASE_' have been removed).

Please test on as many platforms as possible!


    Werner