[musl] IFUNC support

[Maxim Blinov <maxim.a.blinov@gmail.com>]

Hi all,

I just wanted to clarify the current status on IFUNCs, specifically
when generated by the compiler when using the `target_clones` c
function attribute.

Am I correct that this is not currently supported by musl? If so,
would musl ever support this feature, or is it rejected as a matter of
principle? And lastly, if it is possible, what would it take to
support this feature?

I googled around for some previous discussions on the subject and
found https://www.openwall.com/lists/musl/2022/08/23/7, and also
https://www.openwall.com/lists/musl/2014/11/11/2, which reports IFUNCs
as "One feature musl intentionally does not yet support", but I
suppose I wanted to ask again since this was from 2014 and perhaps
something has changed since then.

I originally stumbled on this issue by observing that the musl dynamic
linker, for x86_64, currently errors out on IFUNC symbols with

```
unknown relocation 37
```

And on RISC-V it throws up with

```
unsupported relocation type 58
```

which corresponds with the R_RISCV_IRELATIVE relocation.

BR,
Maxim