xfstests: some refinements on "make depend"

Make it so "make depend" is a generic target, like "make clean".

Each Makefile has a "depend" target that indicates whether making
dependencies means creating ".dep" or creating ".ltdep" (or, I
suppose, both, though none do that right now).  Both files get
created even if there are no CFILES to scan (to ensure the target
up-to-date).  The "default" target now depends on "depend" (there is
no "ltdepend" any more).

Remove the "depend" and "ltdepend" definitions from the "buildrules"
file; only the actual generated files (".dep" and ".ltdep") remain
as generic targets.  The "depend' target is still defined as phony.

Do a shell trick when expanding the value of CFILES, to avoid a
problem that occurs if it is created by "make" by concatentating two
empty strings.  The problem was that in that case CFILES will
contain a space, and that wasn't getting treated as empty as
desired.

Make the rule for tool/lib dependencies more generic, to reflect the
general desire that "lib" subdirectories need to be built before
things in the "tool" subdirectories.

Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

ltp/Makefile

@@ -33,6 +33,8 @@ endif
 
 default: depend $(TARGETS)
 
+depend: .dep
+
 include $(BUILDRULES)
 
 $(TARGETS): $(LIBTEST)