[Qt] Add a no-op thread helper for other platforms

platform/qt/src/thread.cpp

@@ -0,0 +1,19 @@
+#include <mbgl/util/platform.hpp>
+
+#include <string>
+
+namespace mbgl {
+namespace platform {
+
+std::string getCurrentThreadName() {
+    return "unknown";
+}
+
+void setCurrentThreadName(const std::string&) {
+}
+
+void makeThreadLowPriority() {
+}
+
+} // namespace platform
+} // namespace mbgl