Use ART_MODULE_BUILD_FROM_SOURCE instead soong config variable

When product configuration is converted to Starlark, soong config
variables will be stored in a dictionary and won't be able to be
specified directly on the command line. Use a regular variable
that controls the soong config variable.

Bug: 220940864
Test: Presubmits
Change-Id: I5622d9e626e2cf84afe67cd2a214530e64cefc3e
diff --git a/build/Android.common_path.mk b/build/Android.common_path.mk
index 962f691..6ab002a 100644
--- a/build/Android.common_path.mk
+++ b/build/Android.common_path.mk
@@ -22,12 +22,12 @@
 # relate to them, because `m checkbuild` complains on rules with nonexisting
 # dependencies, even if they won't get called.
 # TODO(b/172480617): Remove this when ART sources are no longer in platform manifests.
-ifeq (true,$(SOONG_CONFIG_art_module_source_build))
+ifeq (true,$(ART_MODULE_BUILD_FROM_SOURCE))
   my_art_module_source_build := true
-else ifeq (false,$(SOONG_CONFIG_art_module_source_build))
+else ifeq (false,$(ART_MODULE_BUILD_FROM_SOURCE))
   my_art_module_source_build := false
 else
-  $(error SOONG_CONFIG_art_module_source_build is neither true nor false - mk file ordering problem?)
+  $(error ART_MODULE_BUILD_FROM_SOURCE is neither true nor false - mk file ordering problem?)
 endif
 
 ifeq (true,$(my_art_module_source_build))