elf: Fix ld.so SIGSEGV in trace mode with unresolved TLS symbols (BZ 34532)

[Wilco Dijkstra]

Hi Adhemerval,

>  On loongarch and hppa, running ld.so in trace mode on an object with
> dynamic relocations against undefined TLS symbols crashes with SIGSEGV.
>
> Add the same NULL guards used by all other targets.
>
> Checked on loongarch64-linux-gnu-lp64d and hppa-linux-gnu.

LGTM

Cheers,
Wilco