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>
diff --git a/util/cbfstool/common.c b/util/cbfstool/common.c
index 9923ca3..e8c2ccc 100644
--- a/util/cbfstool/common.c
+++ b/util/cbfstool/common.c
@@ -22,6 +22,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -36,7 +37,7 @@
 int is_big_endian(void)
 {
 	static const uint32_t inttest = 0x12345678;
-	uint8_t inttest_lsb = *(uint8_t *)&inttest;
+	const uint8_t inttest_lsb = *(const uint8_t *)&inttest;
 	if (inttest_lsb == 0x12) {
 		return 1;
 	}
@@ -73,7 +74,7 @@
 		return -1;
 	}
 	buffer->size = get_file_size(fp);
-	if (buffer->size == -1) {
+	if (buffer->size == -1u) {
 		fprintf(stderr, "could not determine size of %s\n", filename);
 		fclose(fp);
 		return -1;