Set build flags in branches from original projects

[ar-lex]

Build a branched package only for repositories and architectures which are explicitly enabled in original project avoiding unnecessary wrong builds, failures and unresolvable packages.

Fixes #10793

[adrianschroeter]

this be incompatible, inconsistent and break a lot, esp. maintenance. sorry, flags are the wrong way for this.

[adrianschroeter]

but this code would also not do what the issue speaks about if I see that right.

[hennevogel]

closing, no feedback from submitter.