[clang] [lld] [lld][WebAssembly] Default to -Bdynamic in wasm-ld (PR #206185)

[Alex Crichton via cfe-commits]

alexcrichton wrote:

Ok cool, yeah if compiling with `-shared` still links with `libc.so` by default that's reasonable to me.

Also I had no idea about `clang.cfg`, that's news to me! If that works I'd also be happy to modify it there.

https://github.com/llvm/llvm-project/pull/206185