[Bug d/91628] libdruntime uses glibc internal symbol on s390

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91628

--- Comment #6 from Florian Weimer <fw at gcc dot gnu.org> ---
__tls_get_offset looks like this:

__tls_get_offset:
        la      %r2,0(%r2,%r12)
        jg      __tls_get_addr

The caller should be able to prepare for the la instruction, by subtracting r12
from r2.  (Not sure whose r12 this, and if it's modified by the PLT code.  If
it is, things could get tricky.)