rtld-elf/riscv: Don't allocate static TLS for dynamic TLS

[jrtc27]

Summary

Provided you don't run out of extra static TLS space this should work,
but it's wholly unnecessary and not how things are supposed to be done.

Fixes: 4b1859c0e943 ("Add support for RISC-V architecture.")
MFC after: 1 week

[kib]

Indeed this is not how things are supposed to work. At least on x86, this is how things are. There are vendor libs linked with static TLS model, which happens to be dynamically loaded, and people really want that to work. The libs cannot be recompiled (they come from nvidia).

If you want to keep risc-v "pure", it is up to you.

[jrtc27]

In D50563#1154663, @kib wrote:

Indeed this is not how things are supposed to work. At least on x86, this is how things are. There are vendor libs linked with static TLS model, which happens to be dynamically loaded, and people really want that to work. The libs cannot be recompiled (they come from nvidia).

If you want to keep risc-v "pure", it is up to you.

It'd be nice if we hadn't gone down that road, but every arch seems to be supporting the extra static TLS space, RISC-V included, so I'm leaving that in for TPREL64, it's not that big a deal (though the infrastructure to support distributing static TLS out to other threads is quite horrifying)