silence a bunch of format-zero-length warnings

This can be observed in many versions of gcc and still exists with 4.9.0:

  wt-status.c: In function ‘wt_status_print_unmerged_header’:
  wt-status.c:191:2: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    status_printf_ln(s, c, "");
    ^

The user have long been told to pass -Wno-format-zero-length, but a
patch that avoids warning altogether is not too noisy, so let's do
so.
Signed-off-by: NFelipe Contreras <felipe.contreras@gmail.com>
Acked-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -805,7 +805,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 				committer_ident.buf);
 
 		if (ident_shown)
-			status_printf_ln(s, GIT_COLOR_NORMAL, "");
+			status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
 
 		saved_color_setting = s->use_color;
 		s->use_color = 0;

wt-status.c

@@ -187,7 +187,7 @@ static void wt_status_print_unmerged_header(struct wt_status *s)
 	} else {
 		status_printf_ln(s, c, _("  (use \"git add/rm <file>...\" as appropriate to mark resolution)"));
 	}
-	status_printf_ln(s, c, "");
+	status_printf_ln(s, c, "%s", "");
 }
 
 static void wt_status_print_cached_header(struct wt_status *s)
@@ -203,7 +203,7 @@ static void wt_status_print_cached_header(struct wt_status *s)
 		status_printf_ln(s, c, _("  (use \"git reset %s <file>...\" to unstage)"), s->reference);
 	else
 		status_printf_ln(s, c, _("  (use \"git rm --cached <file>...\" to unstage)"));
-	status_printf_ln(s, c, "");
+	status_printf_ln(s, c, "%s", "");
 }
 
 static void wt_status_print_dirty_header(struct wt_status *s,
@@ -222,7 +222,7 @@ static void wt_status_print_dirty_header(struct wt_status *s,
 	status_printf_ln(s, c, _("  (use \"git checkout -- <file>...\" to discard changes in working directory)"));
 	if (has_dirty_submodules)
 		status_printf_ln(s, c, _("  (commit or discard the untracked or modified content in submodules)"));
-	status_printf_ln(s, c, "");
+	status_printf_ln(s, c, "%s", "");
 }
 
 static void wt_status_print_other_header(struct wt_status *s,
@@ -234,12 +234,12 @@ static void wt_status_print_other_header(struct wt_status *s,
 	if (!s->hints)
 		return;
 	status_printf_ln(s, c, _("  (use \"git %s <file>...\" to include in what will be committed)"), how);
-	status_printf_ln(s, c, "");
+	status_printf_ln(s, c, "%s", "");
 }
 
 static void wt_status_print_trailer(struct wt_status *s)
 {
-	status_printf_ln(s, color(WT_STATUS_HEADER, s), "");
+	status_printf_ln(s, color(WT_STATUS_HEADER, s), "%s", "");
 }
 
 #define quote_path quote_path_relative
@@ -767,7 +767,7 @@ static void wt_status_print_other(struct wt_status *s,
 	string_list_clear(&output, 0);
 	strbuf_release(&buf);
 conclude:
-	status_printf_ln(s, GIT_COLOR_NORMAL, "");
+	status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
 }
 
 void wt_status_truncate_message_at_cut_line(struct strbuf *buf)
@@ -849,7 +849,7 @@ static void wt_status_print_tracking(struct wt_status *s)
 		color_fprintf_ln(s->fp, color(WT_STATUS_HEADER, s), "%c",
 				 comment_line_char);
 	else
-		fprintf_ln(s->fp, "");
+		fputs("", s->fp);
 }
 
 static int has_unmerged(struct wt_status *s)
@@ -1265,7 +1265,7 @@ void wt_status_print(struct wt_status *s)
 				on_what = _("Not currently on any branch.");
 			}
 		}
-		status_printf(s, color(WT_STATUS_HEADER, s), "");
+		status_printf(s, color(WT_STATUS_HEADER, s), "%s", "");
 		status_printf_more(s, branch_status_color, "%s", on_what);
 		status_printf_more(s, branch_color, "%s\n", branch_name);
 		if (!s->is_initial)
@@ -1278,9 +1278,9 @@ void wt_status_print(struct wt_status *s)
 	free(state.detached_from);
 
 	if (s->is_initial) {
-		status_printf_ln(s, color(WT_STATUS_HEADER, s), "");
+		status_printf_ln(s, color(WT_STATUS_HEADER, s), "%s", "");
 		status_printf_ln(s, color(WT_STATUS_HEADER, s), _("Initial commit"));
-		status_printf_ln(s, color(WT_STATUS_HEADER, s), "");
+		status_printf_ln(s, color(WT_STATUS_HEADER, s), "%s", "");
 	}
 
 	wt_status_print_updated(s);
@@ -1297,7 +1297,7 @@ void wt_status_print(struct wt_status *s)
 		if (s->show_ignored_files)
 			wt_status_print_other(s, &s->ignored, _("Ignored files"), "add -f");
 		if (advice_status_u_option && 2000 < s->untracked_in_ms) {
-			status_printf_ln(s, GIT_COLOR_NORMAL, "");
+			status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
 			status_printf_ln(s, GIT_COLOR_NORMAL,
 					 _("It took %.2f seconds to enumerate untracked files. 'status -uno'\n"
 					   "may speed it up, but you have to be careful not to forget to add\n"