Dynamic libraries on OpenBSD

Hello,

I'm working on a tool for cross-compiling an OpenBSD system from Linux and libtool is causing some issues with shared libraries. My Linux system doesn't have `/usr/libexec/ld.so`, so libtool always claims that the target does not support shared libraries.

I saw there was a patch submitted that fixed this earlier this year, but broke long unsupported architectures without elf and dynamic linking: https://lists.gnu.org/archive/html/libtool-patches/2024-01/msg00094.html

I would support merging that patch as-is. If someone with a vax/m88k/sh machine wants to use modern libtool then adding a hardcoded workaround should be easy with their hardware to test.

Thanks,
Artemis