[6.0] Fix build error

```
ninja: error: 'test/swiftStdlibCollectionUnittest-wasi', needed by 'test/CMakeFiles/check-swift-wasi-wasm32-custom', missing and no known rule to make it
```

Author: kateinoigakukun

schemes/release-6.0/build/build-target-toolchain.sh

@@ -120,7 +120,7 @@ build_target_toolchain() {
     -D SWIFT_RUNTIME_CRASH_REPORTER_CLIENT=NO \
     -D SWIFT_STDLIB_INSTALL_PARENT_MODULE_FOR_SHIMS=NO \
     -D SWIFT_BUILD_DYNAMIC_SDK_OVERLAY=NO \
-    -D SWIFT_BUILD_STATIC_SDK_OVERLAY=NO \
+    -D SWIFT_BUILD_STATIC_SDK_OVERLAY=YES \
     -D SWIFT_PATH_TO_SWIFT_SYNTAX_SOURCE="$SOURCE_PATH/swift-syntax" \
     -D SWIFT_PATH_TO_STRING_PROCESSING_SOURCE="$SOURCE_PATH/swift-experimental-string-processing" \
     -G Ninja \