Don't set SWT_NO_INTEROP on WASI. (#1512)

The toolchain on the release/6.3 branch has regressed because we are
inadvertently setting `SWT_NO_INTEROP` on WASI in the CMake build but
not in the SwiftPM manifest. This change was unintentional.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

cmake/modules/shared/CompilerSettings.cmake

@@ -53,7 +53,7 @@ if(SWT_TESTING_LIBRARY_VERSION)
   add_compile_definitions("$<$<COMPILE_LANGUAGE:CXX>:SWT_TESTING_LIBRARY_VERSION=\"${SWT_TESTING_LIBRARY_VERSION}\">")
 endif()
 
-if(NOT BUILD_SHARED_LIBS)
+if((NOT BUILD_SHARED_LIBS) && (NOT CMAKE_SYSTEM_NAME STREQUAL WASI))
   # When building a static library, Interop is not supported at this time
   add_compile_definitions("SWT_NO_INTEROP")
 endif()