Build the ART modules from source if they are listed in

TARGET_BUILD_APPS.

Test: Run build_mainline_modules.sh and check that
      SOONG_CONFIG_art_module_source_build is true even if the fallback
      default is false.
Bug: 172480615
Change-Id: Ie0e9566d4d09b1e54af00c06021aa355adcf0a1a