setup: Break out common 'options' blocks for kdesrc-build-setup to always use.

This change should address the immediate breakage that a user had when
using kdesrc-build-setup, choosing no major module groups, and then
using kdesrc-build to eventually build bluez-qt.

In that case, bluez-qt had an 'options' block in
kf5-frameworks-build-include to address the error he'd experienced,
however since kdesrc-build-setup didn't generate a include to that file,
the options weren't picked up either. kdesrc-build later found the
module via include-dependencies and built it anyways.

To fix this, break out "always-set" options into a dedicated file
(kf5-common-options-build-include) and include that from
kdesrc-build-setup-generated files always.

I moved these from kf5-frameworks-build-include so I added an include
from that file back to kf5-common-options-build-include for backwards
compatibility for existing users. This relies on duplicate options
blocks continuing to work (similar to C++'s One Definition Rule) so I've
documented that in the code for now.

CCBUG:426219