Surround "#define DEBUG 0" with "#ifndef DEBUG..#endif"

Otherwise "make CFLAGS=-DDEBUG=1" is cumbersome to run.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

blame.c

@@ -18,7 +18,9 @@
 #include "revision.h"
 #include "xdiff-interface.h"
 
+#ifndef DEBUG
 #define DEBUG 0
+#endif
 
 static const char blame_usage[] = "git-blame [-c] [-l] [-t] [-S <revs-file>] [--] file [commit]\n"
 	"  -c, --compatibility Use the same output mode as git-annotate (Default: off)\n"
@@ -232,6 +234,9 @@ static void print_map(struct commit *cmit, struct commit *other)
 	    util2->num_lines ? util->num_lines : util2->num_lines;
 	int num;
 
+	if (print_map == NULL)
+		; /* to avoid "unused function" warning */
+
 	for (i = 0; i < max; i++) {
 		printf("i: %d ", i);
 		num = -1;

cache-tree.c

@@ -2,7 +2,9 @@
 #include "tree.h"
 #include "cache-tree.h"
 
+#ifndef DEBUG
 #define DEBUG 0
+#endif
 
 struct cache_tree *cache_tree(void)
 {