Build the ART module from source if other Mainline modules are.

Test: env MODULES_BUILD_FROM_SOURCE=true \
        TARGET_PRODUCT=cf_x86_64_phone build/soong/soong_ui.bash \
        --dumpvar-mode SOONG_CONFIG_art_module_source_build
  returns true
Test: env TARGET_PRODUCT=cf_x86_64_phone build/soong/soong_ui.bash \
        --dumpvar-mode SOONG_CONFIG_art_module_source_build
  returns false
Bug: 191978129
Change-Id: I718d3878e9d5f5e710fa3d835a209184b633af48