Stop linking libdl.a into static bins

libdl.a has a no-op dlopen, which breaks static libraries that need a real
dlopen. Instead of automatically linking libdl.a into static executables,
make it optional.

Until recently, the libunwind_llvm.a unwinder, used on arm32, needed the
no-op dladdr, but it's now built using -D_LIBUNWIND_USE_DLADDR=0.

The HWASan run-time uses dlsym and dladdr, so add a libdl dependency for
HWASan-built static binaries. We could also remove the dependency from
libclang_rt.hwasan_static-*.a, but this is also easy to do.

Bug: http://b/141485154
Test: bionic unit tests, device boots, verify that static and dynamic
   executables can throw/catch an exception
Test: verify that a static executable using dlopen doesn't link (unless it
   adds an explicit dependency on libdl)

Change-Id: Ic52c3f336b671b4ed335e99c94a64dfe8614b618