Drop whole_static_libs for libasync_safe and clean up static linking of
libsigchain.

whole_static_libs is no longer necessary when libsigchain is a DSO, and
this avoids reexporting all the Bionic headers in the ART SDK.

Test: build/soong/scripts/build-aml-prebuilts.sh art-module-sdk
      unzip -v out/aml/soong/mainline-sdks/art-module-sdk-current.zip
  Check that no Bionic headers are left.
Test: m droid continuous_instrumentation_tests \
       continuous_instrumentation_tests_api_coverage \
       continuous_native_tests device-tests platform_tests
Bug: 142944043
Change-Id: If0982e8bd72f74ed12c270361579e81101de3612
2 files changed