configure lines should support variables

After commit 8cdf60fe6492490561cd6798901b201903ff6ab2 the configure lines are now coded in the platform configuration files.

The configure lines used to be generated by expanding variables in coin, such as the installation prefix or based on feature flags. Now the paths such as c:\Users\qt\work\install are hard-coded and single feature flags that expanded to multiple options are now fully expanded.

By hard-coding the installation path in the configuration files, they cannot be changed anymore unless they are replaced with a variable or a force-push is used.

This is because coin needs to be intrinsically aware of the location in order to produce the artifact archives. So changing it in coin would produce empty archives as the configure line continues to instruct the build system to install to a different location. Such a coin update would not pass. Changing it in the platform configuration files would mean coin would archive an empty directory as it thinks the data is somewhere else and the change would also not pass. In order to change the location, either coin and qt5 changes across all branches must be force-pushed in Gerrit.

It would be much better if the configure syntax would be changed to support variables again, so that the lines could be changed to use -prefix .InstallPrefix for example.

Similarly, the mapping of feature to configure parameter should be stored in a central configuration file in qt5 instead of duplicated in each line, as changing many lines is more error prone and harder to review than a single central change. This becomes particularly beneficial when features expand to multiple options.

I'm filing this as a bug instead of a suggestion given the "deadlock" the location hard-coding has introduced.

I think the ticket can be closed when hard-coded paths and features are replaced with variables.