Reorganize %install phase.
The %install phase is reorganized into 3 distinct phases, the
first phase where files are modified, a second phase where file
lists are generated, and a final phase where files are only
removed based on list information.
This cleanup makes it very clear when we are done installing
files, and therefore creates a place where we can put ABI
instrumentation to compare the resulting ABI before stripping
and debuginfo generation.
No ABI instrumentation is added by this patch, and before-and-after
testing verifies the %install phase remains functionally the same.