yuzu/CMakeLists: Disable implicit QString conversions

Now that all of our code is compilable with implicit QString
conversions, we can enforce it at compile-time by disabling them.

src/yuzu/CMakeLists.txt

@@ -155,6 +155,10 @@ target_compile_definitions(yuzu PRIVATE
     # Use QStringBuilder for string concatenation to reduce
     # the overall number of temporary strings created.
     -DQT_USE_QSTRINGBUILDER
+
+    # Disable implicit conversions from/to C strings
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
 )
 
 if (YUZU_ENABLE_COMPATIBILITY_REPORTING)