[WPE] Unreviewed, fix build after 294837@main

https://bugs.webkit.org/show_bug.cgi?id=292917

Function 'setClipboardContentFromSpan' should be only defined if WPE_PLATFORM
is enabled.

* Source/WebKit/UIProcess/wpe/WebPasteboardProxyWPE.cpp:

Canonical link: https://commits.webkit.org/294955@main

Author: dpino

Source/WebKit/UIProcess/wpe/WebPasteboardProxyWPE.cpp

@@ -111,11 +111,13 @@ void WebPasteboardProxy::readBuffer(IPC::Connection&, const String&, const Strin
     completionHandler({ });
 }
 
+#if ENABLE(WPE_PLATFORM)
 static void setClipboardContentFromSpan(WPEClipboardContent* content, const char* type, const std::span<const char>& text)
 {
     GRefPtr<GBytes> bytes = adoptGRef(g_bytes_new(text.data(), text.size()));
     wpe_clipboard_content_set_bytes(content, type, bytes.get());
 }
+#endif
 
 void WebPasteboardProxy::writeToClipboard(const String&, SelectionData&& selectionData)
 {