Glibc defines d_ptr/d_val to be a relocated address on most
architectures, except for riscv and mips where it is just an offset from
the binary load address. So we need to convert strtab from an offset
into a pointer for riscv and mips.
Internally within glibc there is the D_PTR macro for doing this, which
relies on private data hidden in an ABI-unstable part of link_map. So
we can't use the same conditional logic as glibc does internally.
Our solution is to detect when strtab is unreasonably low (below the
address of our binary) and so it must be an unrelocated offset. In that
case we just do the relocation manually.
Fixes: #6528 (closed)