Use the functions intended for adding Soong config variables.

Test: m
Bug: 172480615
Change-Id: I04ead1eed802747aa7eea5c7b354d7cc3d05c40f
diff --git a/BoardConfigCommon.mk b/BoardConfigCommon.mk
index 2dd5ec3..e741375 100644
--- a/BoardConfigCommon.mk
+++ b/BoardConfigCommon.mk
@@ -31,6 +31,5 @@
 # tree.
 # TODO(b/174997203): Clean this up when there is a better way to switch between
 # prebuilts and sources.
-SOONG_CONFIG_NAMESPACES += art_module
-SOONG_CONFIG_art_module += source_build
-SOONG_CONFIG_art_module_source_build := true
+$(call add_soong_config_namespace,art_module)
+$(call add_soong_config_var_value,art_module,source_build,true)
diff --git a/art_module/art_module.mk b/art_module/art_module.mk
index 4366345..d8074ed 100644
--- a/art_module/art_module.mk
+++ b/art_module/art_module.mk
@@ -20,6 +20,5 @@
 # tree.
 # TODO(b/174997203): Clean up the art_module_* products when there is a better
 # way to switch between prebuilts and sources.
-SOONG_CONFIG_NAMESPACES += art_module
-SOONG_CONFIG_art_module += source_build
-SOONG_CONFIG_art_module_source_build := true
+$(call add_soong_config_namespace,art_module)
+$(call add_soong_config_var_value,art_module,source_build,true)