qt-everywhere-src-5.15.1/qtbase/mkspecs/features/win32/windows_vulkan_sdk.prf

isEmpty(QMAKE_INCDIR_VULKAN) {
    # Pick up the VULKAN_SDK env var set by the LunarG SDK so that the Vulkan
    # headers are found out-of-the-box on typical Windows setups.
    QMAKE_INCDIR_VULKAN = $$(VULKAN_SDK)/include

    # Do not add default include paths as that can knock std headers
    # out of their stride due to their usage of #include_next.
    contains(QMAKE_DEFAULT_INCDIRS, $$QMAKE_INCDIR_VULKAN): \
        QMAKE_INCDIR_VULKAN =

    # Do not export the include dir but resolve it on every qmake call.
    QMAKE_EXPORT_INCDIR_VULKAN = -
}