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: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6528
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2718>
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