make it possible to parameterize dependencies

Module {
    name: "cpp"
    // parameters are just specially scoped property declarations.
    // the syntax is consistent with Constraints (see QBS-995), and shares the namespace with them.
    Parameter {
        // no default value, because it is different for each product type.
        // so let the Rules decide themselves.
        property bool link
    }
    Parameter {
        property bool wholeArchive: false
    }
    Parameter {
        property bool useHeaders: true
    }
}

Product {
    productTypes: [ "plugin", cpp.static ? "staticLibrary" : "dynamicLibrary" ]
    Depends {
        name: "cpp"
    }
    cpp.static: false
    Export {
        Parameters {
            cpp.link: cpp.static
        }
    }
}

Plugin {
    name: "myPlugin1"
    // inherits the default parameter value from Plugin
}

Module {
    name: "myPlugin1"
    Parameters {
        cpp.link: false
    }
    ...
}

Plugin {
    name: "myPlugin2"
    Export {
        Parameters {
            cpp.link: true  // i'm a funny plugin, i want to be linked always
        }
    }
}

Product {
    Depends {
        // not linked
        name: "myPlugin1"
    }
    Depends {
        // linked
        name: "myPlugin2"
    }
    Depends {
        name: "OpenSSL"
        // we don't want to link it, and we have our own function prototypes
        // (openssl is unable to keep binary compat anyway)
        cpp.useHeaders: false
        cpp.link: false
    }
    Depends {
        name: "OpenGL"
        // we don't want to link it, but we want to use its headers for compilation
        cpp.link: false
    }
}

Product {
    DefaultParameters {
        productTypes: ["plugin"]
        cpp.link: true
    }
    Depends {
        // linked
        name: "myPlugin1"
    }
}