[QBS] RFC pkgconfig support

[Joerg Bornemann]

Here's a sketch of how we could add pkgconfig support (or other 
configure-like stuff) to qbs. (The used Process "class" doesn't exist yet.)

---myapp.qbp---
Application {
     name: "myapp"
     Depends { name: "pkconfig" }
     pkconfig.packages: ["opengl", "zlib"]
}

---pkconfig/module.qbs---
Module {
     property var binary: "pkgconfig"
     property var packages

     Depends { name: "cpp" }

     cpp.cxxflags: cpp.cflags
     cpp.cflags: {
         var p = new Process();
         var exitCode = p.start(binary, "--cflags");
         var output = p.readAll();
         return output;
     }

     cpp.ldflags: {
         var p = new Process();
         var exitCode = p.start(binary, "--libs");
         var output = p.readAll();
         return output;
     }
}

Comments appreciated.


Jörg