gl_device: Use a more robust way to use strict context mode

Instead of checking a environment variable which may not actually
exist or is just wrong, ask QT if it's running on the wayland
platform.

src/core/frontend/emu_window.h

@@ -131,6 +131,10 @@ public:
         return active_config;
     }
 
+    bool StrictContextRequired() const {
+        return strict_context_required;
+    }
+
     /**
      * Requests the internal configuration to be replaced by the specified argument at some point in
      * the future.
@@ -207,6 +211,8 @@ protected:
 
     WindowSystemInfo window_info;
 
+    bool strict_context_required = false;
+
 private:
     /**
      * Handler called when the minimal client area was requested to be changed via SetConfig.