[lld][WebAssembly] Always search *.so for -Bdynamic (#84288)

Search *.so libraries regardless of -pie to make it a bit more
straightforward to build non-pie dynamic-linked executables.

Flip the default to -Bstatic (unless -pie or -shared is specified) as I
think it's what most users expect for the default as of today.
The assumption here is that, because dynamic-linking is not widely used
for WebAssembly, the most users do not specify -Bdynamic or -Bstatic,
expecting static link.
Although the recent wasi-sdk ships *.so files, there are not many wasm
runtimes providing the support of dynamic-linking. (only emscripten and
toywasm as far as i know.)