Dynamic linker is explicitly added to runtime APEX

Bionic libs are already in the runtime APEX. Since dynamic linker has to
be in sync with the bionic libs, the linker is also added to the APEX.

Bug: 120266448
Test: m com.android.runtime.debug
Examine the built APEX and check that linker and linker64 exist under
./bin directory

Change-Id: I7d2e0f04d9fbe2082797a73e2c27f406d96f1ac0