Identifier for win64 configuration in Qmake

I do it like this

win32 {

    ## Windows common build here

    !contains(QMAKE_TARGET.arch, x86_64) {
        message("x86 build")

        ## Windows x86 (32bit) specific build here

    } else {
        message("x86_64 build")

        ## Windows x64 (64bit) specific build here

    }
}