sysbuild: Add support for COMPILER_WARNINGS_AS_ERRORS

Adds support for the Kconfig option to enable compiler warnings
being treated as errors in all images that are build. This is a
sticky-set option which means enabling it in sysbuild will
enable it in all images, if it is then disabled in sysbuild it
will not be disabled in any of the images as a result and would
need to be manually unselected.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

share/sysbuild/Kconfig

@@ -42,3 +42,9 @@ config WARN_DEPRECATED
 	  features are enabled.
 
 rsource "images/Kconfig"
+
+menu "Build options"
+
+rsource "build/Kconfig"
+
+endmenu

share/sysbuild/build/Kconfig

@@ -0,0 +1,8 @@
+# Copyright (c) 2024 Nordic Semiconductor
+#
+# SPDX-License-Identifier: Apache-2.0
+
+config COMPILER_WARNINGS_AS_ERRORS
+	bool "Treat warnings as errors"
+	help
+	  Turn on "warning as error" toolchain flags for all images if set.

share/sysbuild/cmake/modules/sysbuild_extensions.cmake

@@ -372,11 +372,14 @@ function(ExternalZephyrProject_Add)
     set_target_properties(${ZBUILD_APPLICATION} PROPERTIES MAIN_APP True)
   endif()
 
+  set(image_default "${CMAKE_SOURCE_DIR}/image_configurations/ALL_image_default.cmake")
+
   if(DEFINED ZBUILD_APP_TYPE)
-    set(image_default "${CMAKE_SOURCE_DIR}/image_configurations/${ZBUILD_APP_TYPE}_image_default.cmake")
-    set_target_properties(${ZBUILD_APPLICATION} PROPERTIES IMAGE_CONF_SCRIPT ${image_default})
+    list(APPEND image_default "${CMAKE_SOURCE_DIR}/image_configurations/${ZBUILD_APP_TYPE}_image_default.cmake")
   endif()
 
+  set_target_properties(${ZBUILD_APPLICATION} PROPERTIES IMAGE_CONF_SCRIPT "${image_default}")
+
   if(DEFINED ZBUILD_BOARD)
     # Only set image specific board if provided.
     # The sysbuild BOARD is exported through sysbuild cache, and will be used

share/sysbuild/image_configurations/ALL_image_default.cmake

@@ -0,0 +1,10 @@
+# Copyright (c) 2024 Nordic Semiconductor
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# This sysbuild CMake file sets the sysbuild controlled settings as properties
+# on all images.
+
+if(SB_CONFIG_COMPILER_WARNINGS_AS_ERRORS)
+  set_config_bool(${ZCMAKE_APPLICATION} CONFIG_COMPILER_WARNINGS_AS_ERRORS y)
+endif()