Reenable --disable-gpu on Mac

Avoids corruption issues when GL context sharing between Qt and
WebEngine fails. 5K macs (the previous corruption issue) still work,
thanks to our Qt patches.

src/main.cpp

@@ -85,9 +85,7 @@ void ShowLicenseInfo()
 
 /////////////////////////////////////////////////////////////////////////////////////////
 QStringList g_qtFlags = {
-#ifndef Q_OS_MAC
   "--disable-gpu",
-#endif
   "--disable-web-security"
 };