* Add a CI check for testing toolchains as-distributed
One aspect of testing lost in the CMake-based migration is the ability
to test the toolchains as distributed in release artifacts. Tests use
`--sysroot` and `-resource-dir` (soon) to customize how the host
compiler runs but this means that it would be possible to regress the
default sysroot theoretically. To rectify this situation this commit
adds a new CI test which uses the release artifacts of previous steps to
build a `wasi-sdk-*.tar.gz` tarball which is then extracted and tested
as-is. A new flag was added to the cmake configuration to avoid
depending on fresh sysroot libraries for tests and instead test the host
toolchain.
* Fix version.py script running
* Fix artifact download
* Add ninja
* Update submodules in new test job
* Only add extra options for libcxx build
Otherwise the test directory seems like it inherits these options which
isn't desired when testing the host toolchain.