Add OS=wasi as supported to embedded/lit.local.cfg

There's a predefined list of supported platforms that WASI should be added now that it has an official Embedded Swift SDK.

Author: MaxDesiatov

test/embedded/lit.local.cfg

@@ -20,7 +20,7 @@ if 'embedded_stdlib' not in config.available_features:
   config.unsupported = True
 
 # (3) Restrict Embedded Swift tests only to the currently supported set of test target OS's, skip them otherwise.
-supported_test_os_list = ["OS=macosx", "OS=linux-gnu", "OS=none-eabi", "OS=none-elf"]
+supported_test_os_list = ["OS=macosx", "OS=linux-gnu", "OS=none-eabi", "OS=none-elf", "OS=wasi"]
 if config.available_features.intersection(set(supported_test_os_list)) == set():
   config.unsupported = True