am: move advice.amWorkDir parsing back to advice.c

The only benefit from this move (apart from cleaner code) is that
advice.amWorkDir should now show up in `git help --config`. There
should be no regression since advice config is always read by the
git_default_config().

While at there, use advise() like other code. We now get "hint: "
prefix and the output is stderr instead of stdout (which is also the
reason for the test update because stderr is checked in a following
test and the extra advice can fail it).

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

advice.c

@@ -17,6 +17,7 @@ int advice_implicit_identity = 1;
 int advice_detached_head = 1;
 int advice_set_upstream_failure = 1;
 int advice_object_name_warning = 1;
+int advice_amworkdir = 1;
 int advice_rm_hints = 1;
 int advice_add_embedded_repo = 1;
 int advice_ignored_hook = 1;
@@ -68,6 +69,7 @@ static struct {
 	{ "detachedHead", &advice_detached_head },
 	{ "setupStreamFailure", &advice_set_upstream_failure },
 	{ "objectNameWarning", &advice_object_name_warning },
+	{ "amWorkDir", &advice_amworkdir },
 	{ "rmHints", &advice_rm_hints },
 	{ "addEmbeddedRepo", &advice_add_embedded_repo },
 	{ "ignoredHook", &advice_ignored_hook },

advice.h

@@ -17,6 +17,7 @@ extern int advice_implicit_identity;
 extern int advice_detached_head;
 extern int advice_set_upstream_failure;
 extern int advice_object_name_warning;
+extern int advice_amworkdir;
 extern int advice_rm_hints;
 extern int advice_add_embedded_repo;
 extern int advice_ignored_hook;

builtin/am.c

@@ -1827,15 +1827,11 @@ static void am_run(struct am_state *state, int resume)
 		}
 
 		if (apply_status) {
-			int advice_amworkdir = 1;
-
 			printf_ln(_("Patch failed at %s %.*s"), msgnum(state),
 				linelen(state->msg), state->msg);
 
-			git_config_get_bool("advice.amworkdir", &advice_amworkdir);
-
 			if (advice_amworkdir)
-				printf_ln(_("Use 'git am --show-current-patch' to see the failed patch"));
+				advise(_("Use 'git am --show-current-patch' to see the failed patch"));
 
 			die_user_resolve(state);
 		}

t/t4254-am-corrupt.sh

@@ -25,7 +25,7 @@ test_expect_success setup '
 #   fatal: unable to write file '(null)' mode 100644: Bad address
 # Also, it had the unwanted side-effect of deleting f.
 test_expect_success 'try to apply corrupted patch' '
-	test_must_fail git am bad-patch.diff 2>actual
+	test_must_fail git -c advice.amWorkDir=false am bad-patch.diff 2>actual
 '
 
 test_expect_success 'compare diagnostic; ensure file is still here' '