cbfstool: Clean up in preparation for adding new files

This enables more warnings on the cbfstool codebase and fixes the
issues that surface as a result. A memory leak that used to occur
when compressing files with lzma is also found and fixed.
Finally, there are several fixes for the Makefile:
 - Its autodependencies used to be broken because the target for
   the .dependencies file was misnamed; this meant that Make
   didn't know how to rebuild the file, and so would silently
   skip the step of updating it before including it.
 - The ability to build to a custom output directory by defining
   the obj variable had bitrotted.
 - The default value of the obj variable was causing implicit
   rules not to apply when specifying a file as a target without
   providing a custom value for obj.
 - Add a distclean target for removing the .dependencies file.

BUG=chromium:461875
TEST=Build an image with cbfstool both before and after.
BRANCH=None

Change-Id: I951919d63443f2b053c2e67c1ac9872abc0a43ca
Signed-off-by: Sol Boucher <solb@chromium.org>
Original-Commit-Id: 49293443b4e565ca48d284e9a66f80c9c213975d
Original-Change-Id: Ia7350c2c3306905984cfa711d5fc4631f0b43d5b
Original-Signed-off-by: Sol Boucher <solb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/257340
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-on: http://review.coreboot.org/9937
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/cbfstool/lzma/lzma.c

@@ -142,6 +142,7 @@ int do_lzma_compress(char *in, int in_len, char *out, int *out_len)
 	Write(&os, propsEncoded, LZMA_PROPS_SIZE+8);
 
 	res = LzmaEnc_Encode(p, &os, &is, 0, &LZMAalloc, &LZMAalloc);
+	LzmaEnc_Destroy(p, &LZMAalloc, &LZMAalloc);
 	if (res != SZ_OK) {
 		ERROR("LZMA: LzmaEnc_Encode failed %d.\n", res);
 		return -1;