Fix bionic-unit-tests in arch with binary translator

If binary translator is involved then libc is not place in /system/lib
or /system/lib64.  It's placed into /syste/lib/arm, /system/lib/arm64,
etc.  FUGU is an example of such an architecture.

Support both cases by picking right path at runtime.

Test: run bionic-unit-tests --gtest_filter=dlfcn.dladdr_libc
Change-Id: I8345c0f6c19376ebe5106f9670fd2addeb9b9080