Prefer prebuilts by default.

SOONG_CONFIG_art_module_source_build is true by default instead, to
keep prefering sources.

Test: art/build/update-art-module-prebuilts.sh --local-dist=...
  (Files in this CL writted by updated script.)
Bug: 172480615
Change-Id: Ifedb18e0988307b327dadf2f98b6c603f361c3f2
3 files changed
tree: 63516ae02db279545b1aea986e2447e5c85b021b
  1. SoongConfig.bp
  2. current/