Merge "Change default for source_build config variable to true."

# CrossHost: linux_bionic

# CrossHostArch: x86_64

#   -  Enable Bionic on host as ART needs prebuilts for it.

# VendorVars.art_mdoule.source_build

#   -  TODO(b/172480615): Change default to false when platform uses ART Module

#      prebuilts by default.

cat > ${SOONG_VARS}.new << EOF

{

    "BuildNumberFile": "build_number.txt",

    "VendorVars": {

        "art_module": {

            "source_build": "${ENABLE_ART_SOURCE_BUILD:-false}"

            "source_build": "${ENABLE_ART_SOURCE_BUILD:-true}"

        }

    },