wasm: disable XDG_RUNTIME_DIR warning

XDG is not very relevant on the Web platform.

Change-Id: Ibd885e28da15114d0601c73e34dec556e65cbe75
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/io/qstandardpaths_unix.cpp

@@ -134,7 +134,9 @@ QString QStandardPaths::writableLocation(StandardLocation type)
                     return QString();
                 }
             }
+#ifndef Q_OS_WASM
             qWarning("QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '%s'", qPrintable(xdgRuntimeDir));
+#endif
         } else {
             fileInfo.setFile(xdgRuntimeDir);
             if (!fileInfo.exists()) {