update WM_CLASS instance name from vm_name

src/qt/x11_util.c

@@ -0,0 +1,22 @@
+#include <X11/Xlib.h>
+#include <X11/Xutil.h>
+#include <stdio.h>
+
+#include "x11_util.h"
+
+void set_wm_class(unsigned long window, char *res_name) {
+    Display* display = XOpenDisplay(NULL);
+    if (display == NULL) {
+        return;
+    }
+
+    XClassHint hint;
+    XGetClassHint(display, window, &hint);
+
+    hint.res_name = res_name;
+    XSetClassHint(display, window, &hint);
+
+    // During testing, I've had to issue XGetClassHint after XSetClassHint
+    // to get the window manager to recognize the change.
+    XGetClassHint(display, window, &hint);
+}