1) Add OPT_CFLAGS to allow the warning flags to by overriden by
the command line. Thomas Renninger (trenn@suse.de)
2) Eliminate extraneous spaces from the makefile execution output.
Add dependencies for ACPICA and local headers.
Simplify by using source directory search via "vpath" in order
to eliminate one explicit rule per object/source file.
Update purpose of the makefile and add a warning that these makefiles
are only suitable for generation within the native ACPICA directory
structure (which is different than Linux, for example.)
