[clang] [Driver] Make ELF -nopie specific to OpenBSD (PR #72578)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> -nopie is for the linker. We only use -fno-pie for the compiler.

OK. Then it seems that the driver option `-nopie` for linking should be removed even for OpenBSD?

https://github.com/llvm/llvm-project/pull/72578