hppa/ia64: _dl_symbol_address: add PLT bypass for rtld

This symbol is defined in the ldso, and is used both there and libc.so.
There is no hidden symbol for it though which leads to relocations in
the ldso and the elf/check-localplt test failing.  Add a hidden def for
rtld to fix all of that.

This function/file is only used by hppa & ia64, so no testing is needed
for other arches.