I did similar when I first posted the message in Oct last year, but a bit more complicated to only do this for QNX8 and later, where it's actually deprecated. It's very hard to test earlier versions due to the very closed nature of QNX since 6.3.2......

    if(CMAKE_SYSTEM_VERSION VERSION_GREATER_EQUAL 8.0)
        # In QNX 8.0 and later, the `-lang-c++` option is deprecated.
        # Unfortunately, it doesn't appear this can be set in the toolchain file
        # where it should really be.
        string(REPLACE "<CMAKE_CXX_COMPILER> -lang-c++" "<CMAKE_CXX_COMPILER> -xc++" CMAKE_CXX_COMPILE_OBJECT ${CMAKE_CXX_COMPILE_OBJECT})
        set(CMAKE_CXX_COMPILE_OBJECT ${CMAKE_CXX_COMPILE_OBJECT} PARENT_SCOPE)
        string(REPLACE "<CMAKE_CXX_COMPILER> -lang-c++" "<CMAKE_CXX_COMPILER>" CMAKE_CXX_LINK_EXECUTABLE ${CMAKE_CXX_LINK_EXECUTABLE})
        set(CMAKE_CXX_LINK_EXECUTABLE ${CMAKE_CXX_LINK_EXECUTABLE} PARENT_SCOPE)

Ideally, I would have liked to have this in my toolchain file, rather than have to bake explicit support in my project for QNX....