[lld] Make hashtable entry size configurable (PR #113431)

[Ulrich Weigand via llvm-commits]

uweigand wrote:

> Thanks for the patch, but is this needed? `.hash` is quite obsoleted (https://maskray.me/blog/2022-08-21-glibc-and-dt-gnu-hash)
> 
> We could make a special case to make `--hash-style=both` mean just `gnu` for SystemZ. `sysv` could be made unsupported.

Well, we noticed the problem because the Linux kernel builds the vdso using `--hash-style=both` (or `--hash-style=sysv` on some architectures), and the vdso selftests actually fail if there is no (or an incorrect) `DT_HASH` section.

To avoid any unnecessary differences between architectures, I would prefer for `DT_HASH` to remain supported on s390x as long as it still is supported on other Linux architectures.

https://github.com/llvm/llvm-project/pull/113431