It's now impossible to override list properties on the command line

Since all the module merging stuff, it's now impossible to override list properties on the command line. The values specified on the command line can only be concatenated with the values from modules, but not override them entirely (unless the value comes from a profile, which is unnecessarily verbose and difficult for simple one-off property assignments).

We should have a way to explicitly use the value of a list property from the command line, probably using a new syntax. A possible syntax might be:

qbs qbs.targetOS=:android,linux,unix

...which is similar to the notation used for setting a value in some languages. Or perhaps moving the equals sign to the front:

qbs =qbs.targetOS:android,linux,unix

This specific example relates to QBS-1070, which may have an alternate solution anyways, but I think it is still valuable to solve this for the general case as it may be needed for other properties in certain circumstances.