feat(cmakev2/idf): initialize IDF_TARGET_ARCH build property

Based on the configuration, set the IDF_TARGET build property. This is
also set by cmakev1 and can be used to easily determine the architecture
for the project.

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/cmakev2/idf.cmake

@@ -458,6 +458,24 @@ function(__init_submodules)
     endforeach()
 endfunction()
 
+#[[
+   __init_idf_target_arch()
+
+   Set the IDF_TARGET_ARCH value based on the sdkconfig. This means it must be
+   initialized after the sdkconfig is generated and its CMake version is
+   included.
+#]]
+function(__init_idf_target_arch)
+    if(CONFIG_IDF_TARGET_ARCH_XTENSA)
+        idf_build_set_property(IDF_TARGET_ARCH "xtensa")
+    elseif(CONFIG_IDF_TARGET_ARCH_RISCV)
+        idf_build_set_property(IDF_TARGET_ARCH "riscv")
+    else()
+        # Currently, no architecture is specified for Linux host builds.
+        idf_build_set_property(IDF_TARGET_ARCH "")
+    endif()
+endfunction()
+
 #[[
    The idf_build_properties interface target is exclusively used to store
    information about global build properties and is not linked or used in any
@@ -556,6 +574,10 @@ if(NOT EXISTS "${sdkconfig_cmake}")
 endif()
 include("${sdkconfig_cmake}")
 
+# Initialize the target architecture based on the configuration. Ensure this is
+# done after including the sdkconfig.
+__init_idf_target_arch()
+
 #[[ TODO
 
 Many of the following things are already implemented in PoC !38337, but they