According to the specification:
```
When instantiating a module which is expected to run
with `wasi-threads`, the WASI host must first allocate shared memories to
satisfy the module's imports.
```
Currently, if a test from the spec is executed while having the `multi-module`
feature enabled, WAMR fails with `WASM module load failed: unknown import`.
That happens because spec tests use memory like this:
`(memory (export "memory") (import "foo" "bar") 1 1 shared)`
and WAMR tries to find a registered module named `foo`.
At the moment, there is no specific module name that can be used to identify
that the memory is imported because using WASI threads:
https://github.com/WebAssembly/wasi-threads/issues/33,
so this PR only avoids treating the submodule dependency not being found
as a failure.
4aee3cf14e