CMakeLists: Define QT_USE_QSTRINGBUILDER for the Qt target

This is a compile definition introduced in Qt 4.8 for reducing the total
potential number of strings created when performing string
concatenation. This allows for less memory churn.

This can be read about here:
https://blog.qt.io/blog/2011/06/13/string-concatenation-with-qstringbuilder/

For a change that isn't source-compatible, we only had one occurrence
that actually need to have its type clarified, which is pretty good, as
far as transitioning goes.

src/yuzu/CMakeLists.txt

@@ -151,6 +151,12 @@ target_link_libraries(yuzu PRIVATE common core input_common video_core)
 target_link_libraries(yuzu PRIVATE Boost::boost glad Qt5::OpenGL Qt5::Widgets)
 target_link_libraries(yuzu PRIVATE ${PLATFORM_LIBRARIES} Threads::Threads)
 
+target_compile_definitions(yuzu PRIVATE
+    # Use QStringBuilder for string concatenation to reduce
+    # the overall number of temporary strings created.
+    -DQT_USE_QSTRINGBUILDER
+)
+
 if (YUZU_ENABLE_COMPATIBILITY_REPORTING)
     target_compile_definitions(yuzu PRIVATE -DYUZU_ENABLE_COMPATIBILITY_REPORTING)
 endif()

src/yuzu/game_list_p.h

@@ -95,7 +95,7 @@ public:
             if (row2.isEmpty())
                 return row1;
 
-            return row1 + "\n    " + row2;
+            return QString(row1 + "\n    " + row2);
         }
 
         return GameListItem::data(role);