Build fix for Swift 5.9

Author: kateinoigakukun

Sources/JavaScriptKit/FundamentalObjects/JSObject.swift

@@ -206,8 +206,6 @@ public class JSObject: Equatable {
     /// This allows access to the global properties and global names by accessing the `JSObject` returned.
     public static var global: JSObject { return _global }
 
-    // `JSObject` storage itself is immutable, and use of `JSObject.global` from other
-    // threads maintains the same semantics as `globalThis` in JavaScript.
     @LazyThreadLocal(initialize: {
         return JSObject(id: _JS_Predef_Value_Global)
     })

Sources/JavaScriptKit/ThreadLocal.swift

@@ -78,8 +78,11 @@ final class ThreadLocal<Value>: Sendable {
     }
 #else
     // Fallback implementation for platforms that don't support pthread
-
+    #if compiler(>=5.10)
     nonisolated(unsafe) var wrappedValue: Value?
+    #else
+    var wrappedValue: Value?
+    #endif
 
     init() where Value: AnyObject {
         wrappedValue = nil