QRCodeGen: Exclude unused library from build

The QR Code Generator is only used by design studio
so we can save some cycles during compile time by only
activating it when building DesignStudio.

Change-Id: I248c72e7c2e9ca536026d1647630b6dc9a5f80a0
Reviewed-by: Burak Hancerli <burak.hancerli@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/3rdparty/CMakeLists.txt

@@ -2,7 +2,6 @@ add_subdirectory(cplusplus)
 add_subdirectory(syntax-highlighting)
 add_subdirectory(libvterm)
 add_subdirectory(libptyqt)
-add_subdirectory(qrcodegen)
 add_subdirectory(qtkeychain)
 add_subdirectory(lua)
 add_subdirectory(sol2)
@@ -10,3 +9,7 @@ add_subdirectory(sol2)
 if(WIN32)
     add_subdirectory(winpty)
 endif()
+
+if (BUILD_DESIGNSTUDIO)
+    add_subdirectory(qrcodegen)
+endif()