bisect.c: make show_list() build again

This function only compiles when DEBUG_BISECT is 1, which is often not
the case. As a result there are two commits [1] [2] that break it but
the breakages went unnoticed because the code did not compile by
default. Update the function and include the new header file to make this
function build again.

In order to stop this from happening again, the function is now
compiled unconditionally but exits early unless DEBUG_BISECT is
non-zero. A smart compiler generates no extra code (not even a
function call). But even if it does not, this function does not seem
to be in a hot path that the extra cost becomes a big problem.

[1] bb408ac95d (bisect.c: use commit-slab for commit weight instead of
    commit->util - 2018-05-19)

[2] cbd53a2193 (object-store: move object access functions to
    object-store.h - 2018-05-15)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bisect.c

@@ -13,6 +13,7 @@
 #include "sha1-array.h"
 #include "argv-array.h"
 #include "commit-slab.h"
+#include "object-store.h"
 
 static struct oid_array good_revs;
 static struct oid_array skipped_revs;
@@ -120,14 +121,14 @@ static inline int halfway(struct commit_list *p, int nr)
 	}
 }
 
-#if !DEBUG_BISECT
-#define show_list(a,b,c,d) do { ; } while (0)
-#else
 static void show_list(const char *debug, int counted, int nr,
 		      struct commit_list *list)
 {
 	struct commit_list *p;
 
+	if (!DEBUG_BISECT)
+		return;
+
 	fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 
 	for (p = list; p; p = p->next) {
@@ -145,7 +146,7 @@ static void show_list(const char *debug, int counted, int nr,
 			(flags & TREESAME) ? ' ' : 'T',
 			(flags & UNINTERESTING) ? 'U' : ' ',
 			(flags & COUNTED) ? 'C' : ' ');
-		if (commit->util)
+		if (*commit_weight_at(&commit_weight, p->item))
 			fprintf(stderr, "%3d", weight(p));
 		else
 			fprintf(stderr, "---");
@@ -160,7 +161,6 @@ static void show_list(const char *debug, int counted, int nr,
 		fprintf(stderr, "\n");
 	}
 }
-#endif /* DEBUG_BISECT */
 
 static struct commit_list *best_bisection(struct commit_list *list, int nr)
 {