Add -Bsymbolic to the ld flags when linking the dynamic linker.

We don't need this on architectures other than aarch64, and
we're still investigating why we need it on aarch64, but it
doesn't seem unreasonable to have this flag set when linking
the dynamic linker anyway; it's clearly the intended behavior.

Change-Id: I4fa1b4ae543a818979934bf818eabac03bb9154f