Get rid of dependencies on /system/bin ART binary compat symlinks.

Make the tools/art script try the /apex/com.android.art location first,
for use on device. Also add a symlink for dex2oat to the preferred
bitness in the APEX, just like dalvikvm already has, so the script
works with neither --32 nor --64.

Test: m installclean
      art/tools/buildbot-build.sh --target && \
        art/tools/buildbot-teardown-device.sh && \
        art/tools/buildbot-cleanup-device.sh && \
        art/tools/buildbot-setup-device.sh && \
        art/tools/buildbot-sync.sh
      art/tools/run-libcore-tests.sh --mode=device --variant=X32 libcore.sun.net
      art/tools/run-libcore-tests.sh --mode=device --variant=X64 libcore.sun.net
  with the script temporarily changed to error out on missing dex2oat
Test: rm -r out/host
      art/tools/buildbot-build.sh --host
      art/tools/run-libcore-tests.sh --mode=host --variant=X32 libcore.sun.net
      art/tools/run-libcore-tests.sh --mode=host --variant=X64 libcore.sun.net
  with the script temporarily changed to error out on missing dex2oat
Test: lunch aosp_cf_x86_64_phone
      art/build/apex/runtests.sh --bitness=multilib
Test: lunch aosp_arm
      art/build/apex/runtests.sh
Bug: 155478143
Change-Id: Ie6a6c057c5948d353258882f5a9e0ae921d7bedc
3 files changed