Fix AddressSanitizer link order and multilib setup.

ASan runtime library (when using dynamic linking) must be the first
dependency of the main executable to achieve correct symbol
interposition. This matches how the clang driver works.

In multilib setup, ASan-RT name depends on the target arch:
  /system/lib/libclang_rt.asan-arm-android.so
  /system/lib64/libclang_rt.asan-arm64-android.so

We also set RPATH to /system/lib/asan or /system/lib64/asan
to have a place for ASan-only versions of system libraries.

Change-Id: I937d202077b6e433ba476c075d31be818b662d53