[wasm] Assume WASI is single-threaded and mark global storage nonisolated(unsafe)

Author: kateinoigakukun

Sources/FoundationXML/XMLParser.swift

@@ -471,7 +471,7 @@ open class XMLParser : NSObject {
     open var allowedExternalEntityURLs: Set<URL>?
 
 #if os(WASI)
-    private static var _currentParser: XMLParser?
+    private nonisolated(unsafe) static var _currentParser: XMLParser?
 #endif
 
     internal static func currentParser() -> XMLParser? {