generic: Kconfig: exit on unset symbol

When a target configuration has unser Kconfig symbols, the build will
fail when OpenWrt is compiled with V=s and stdin is connected to a tty.

In case OpenWrt is compiled without either of these preconditions, the
build will uscceed with the symbols in question being unset.

Modify the kernel configuration in a way it fails on unset symbols
regardless of the aformentioned preconditions.

Signed-off-by: David Bauer <mail@david-bauer.net>

include/kernel-build.mk

@@ -132,6 +132,7 @@ define BuildKernel
   $(LINUX_DIR)/.modules: export STAGING_PREFIX=$$(STAGING_DIR_HOST)
   $(LINUX_DIR)/.modules: export PKG_CONFIG_PATH=$$(STAGING_DIR_HOST)/lib/pkgconfig
   $(LINUX_DIR)/.modules: export PKG_CONFIG_LIBDIR=$$(STAGING_DIR_HOST)/lib/pkgconfig
+  $(LINUX_DIR)/.modules: export FAIL_ON_UNCONFIGURED=1
   $(LINUX_DIR)/.modules: $(STAMP_CONFIGURED) $(LINUX_DIR)/.config FORCE
 	$(Kernel/CompileModules)
 	touch $$@

target/linux/generic/hack-5.10/205-kconfig-exit.patch

@@ -0,0 +1,11 @@
+--- a/scripts/kconfig/conf.c
++++ b/scripts/kconfig/conf.c
+@@ -212,6 +212,8 @@ static int conf_sym(struct menu *menu)
+ 				break;
+ 			continue;
+ 		case 0:
++			if (!sym_has_value(sym) && !tty_stdio && getenv("FAIL_ON_UNCONFIGURED"))
++				exit(1);
+ 			newval = oldval;
+ 			break;
+ 		case '?':

target/linux/generic/hack-5.4/205-kconfig-exit.patch

@@ -0,0 +1,11 @@
+--- a/scripts/kconfig/conf.c
++++ b/scripts/kconfig/conf.c
+@@ -212,6 +212,8 @@ static int conf_sym(struct menu *menu)
+ 				break;
+ 			continue;
+ 		case 0:
++			if (!sym_has_value(sym) && !tty_stdio && getenv("FAIL_ON_UNCONFIGURED"))
++				exit(1);
+ 			newval = oldval;
+ 			break;
+ 		case '?':