util/kconfig: Uprev to Linux 6.6's kconfig

Upstream reimplemented KCONFIG_STRICT, just calling it KCONFIG_WERROR.
Therefore, adapt our build system and documentation. Upstream is less
strict at this time, but there's a proposed patch that got imported.

TEST=`util/abuild/abuild -C` output (config.h and
config.build) remains the same. Also, the failure type fixed in
https://review.coreboot.org/c/coreboot/+/11272 can be detected,
which I tested by manually breaking our Kconfig in a similar way.

Change-Id: I322fb08a2f7308b93cff71a5dd4136f1a998773b
Signed-off-by: Patrick Georgi <patrick@coreboot.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79259
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>

util/kconfig/patches/0001-Kconfig-Add-KCONFIG_STRICT-mode.patch

@@ -1,43 +1,18 @@
-From c822f47921feb53b97f48f3aa8d1e843f5099c63 Mon Sep 17 00:00:00 2001
-From: Stefan Reinauer <stefan.reinauer@coreboot.org>
-Date: Fri, 17 Jul 2015 17:26:48 -0700
-Subject: [PATCH] Kconfig: Add KCONFIG_STRICT mode
-
-This is basically a -Werror mode for Kconfig. When exporting
-KCONFIG_STRICT in the Makefile, warnings in Kconfig will produce
-errors instead.
-
-This will make it easier to spot unclean Kconfig files, settings
-and dependencies.
-
-Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
----
- util/kconfig/confdata.c | 8 ++++++++
- 1 file changed, 8 insertions(+)
+Make KCONFIG_WERROR more verbose.
 
 Index: kconfig/confdata.c
 ===================================================================
 --- kconfig.orig/confdata.c
 +++ kconfig/confdata.c
-@@ -437,6 +437,7 @@ load:
- 			if (def == S_DEF_USER) {
- 				sym = sym_find(line + 2 + strlen(CONFIG_));
- 				if (!sym) {
-+					conf_warning("trying to assign non-existent symbol %s", line + strlen(CONFIG_));
- 					conf_set_changed(true);
- 					continue;
- 				}
-@@ -519,6 +520,13 @@ load:
- 	}
+@@ -533,8 +533,10 @@ load:
  	free(line);
  	fclose(in);
-+
-+	name = getenv("KCONFIG_STRICT");
-+	if (name && *name && conf_warnings) {
+ 
+-	if (conf_warnings && werror)
++	if (conf_warnings && werror) {
 +		fprintf(stderr, "\nERROR: %d warnings encountered, and warnings are errors.\n\n", conf_warnings);
-+		return 1;
+ 		exit(1);
 +	}
-+
+ 
  	return 0;
  }
-