RFE: add macros used during a build to SRPM header

[n3npq]

RPM was designed to encapsulate elements necessary for a build into a package reproducibly.

One element that is not encapsulated is the rpm configuration in place during a build. As common operations are refactored out of spec files into configuration, it becomes increasingly important to supply the configuration macros instantiated in order to identify how to build software.

RPM already macros macros used during a build. All that is needed is a loop over all macros (which are already sorted for bsearch(3) retrieval) filtering out unused macros and adding "KEY VALUE" strings in an argv array to be added to a SRPM header.