See: https://github.com/tinygo-org/tinygo/issues/4314
The os package isn't particularly useful on wasm-unknown, but just like
on baremetal systems it's imported by a lot of packages so it should at
least be possible to import this package.
This adds true GOOS=wasip1 support in addition to our existing
-target=wasi support. The old support for WASI isn't removed, but should
be treated as deprecated and will likely be removed eventually to reduce
the test burden.