lucet-wasi-sdk: disable threading in lld (wasi-ld)
lucet-wasi-sdk: disable threading in lld (wasi-ld)

it appears that as of this moment both of the following are true:
* lld's wasm linker may deadlock if linking with threads enabled
* lld's wasm linker builds with threads enabled by default

some references found in tracking this down:
https://bugs.llvm.org/show_bug.cgi?id=37064

the following looks to not be wasm-related in particular:
https://bugs.llvm.org/show_bug.cgi?id=34806

but similar patterns seem to exist in the wasm driver used by lld,
even if they've since been fixed for other targets.

fastly/lucet,fastly/lucet,fastly/lucet,fastly/lucet,fastly/lucet