[REG 5.12.0-5.12.1] qt_libs_gui_private.pri in prebuilt binaries contain local VulkanSDK include path

I'm using official Qt 5.12.1 MSVC 2017 32 bit binaries, installed via the Qt online installer.

Since 5.12.1, I got an unwanted additional include path added to my compiler command line:

`-IC:\VulkanSDK\1.0.51.0\include`

Using 5.12.0, this include does not appear. It is definitly not added by my project files, but instead must come from Qt mkspecs.

Running a grep in mkspecs, listed the following:

`modules/qt_lib_gui_private.pri:QMAKE_INCDIR_VULKAN = C:\\VulkanSDK
1.0.51.0
include`

Is it maybe a private include that accidentally got added somewhere?