[ ~/Code/trash ] $ cat delete-me.pro 
warning("allways")
A {
    warning("configA")
}
B {
    warning("configB")
}
A|B {
    warning("configA || configB")
}
A:B {
    warning("configA && configB")
}
 [ ~/Code/trash ] $ qmake delete-me.pro 
Project WARNING: allways
 [ ~/Code/trash ] $ qmake -config A delete-me.pro 
Project WARNING: allways
Project WARNING: configA
Project WARNING: configA || configB
 [ ~/Code/trash ] $ qmake -config B delete-me.pro 
Project WARNING: allways
Project WARNING: configB
Project WARNING: configA || configB
 [ ~/Code/trash ] $ qmake -config A -config B delete-me.pro 
Project WARNING: allways
Project WARNING: configA
Project WARNING: configB
Project WARNING: configA || configB
Project WARNING: configA && configB