wasi-threads: run test suite (#5907)

* wasi-threads: run test suite

This change enables the running of the wasi-threads [test suite]. It
relies on a Wasmtime CLI binary being available and runs all `*.wasm`
and `*.wat` files present in the test suite directory. The results of
each execution are compared against a JSON spec file with the same base
name as the WebAssembly module. The spec file defines the expected exit
code, e.g.

This commit does not yet build any `*.c` or `*.s` files from the test
suite. That could be done later, perhaps upstream; in the meantime, this
work is still valuable as it lays the foundation for running other WASI
tests from the in-progress [wasi-testsuite] which share the same JSON
spec infrastructure.

[test suite]: https://github.com/WebAssembly/wasi-threads/tree/main/test/testsuite
[wasi-testsuite]: https://github.com/WebAssembly/wasi-testsuite

* review: move testsuite to top-level tests

* fix: remove now-unnecessary wasi-threads test

* fix: update testsuite submodule name

* fix: ignore tests on Windows

prtest:full

* fix: `cfg_attr` syntax

prtest:full

.gitmodules

@@ -13,3 +13,6 @@
 [submodule "crates/wasi-crypto/spec"]
 	path = crates/wasi-crypto/spec
 	url = https://github.com/WebAssembly/wasi-crypto.git
+[submodule "tests/wasi_testsuite/wasi-threads"]
+	path = tests/wasi_testsuite/wasi-threads
+	url = https://github.com/WebAssembly/wasi-threads