Perform some lightweight kclause analysis to determine architectures to try first

[paulgazz]

With the same motivation as #185, one of the challenges for krepair is when the original configuration file is from a different architecture then some lines of code in the patch and the user does not provide an architecture to try. krepair currently tries them all in a fixed order until if finds satisfying coverage constraints. #185 looks at the filename to see if it's from the arch/ directory and starts the architecture search there. But some files are architecture-specific, but are not in the arch/ directory. For instance, Linux commit 7eafa6eed7f1c6d0d7ed2f90792ab6bce462a750 is a powerpc compilation unit in drivers/dma/ppc4xx/adma.c (perhaps more file path heuristics could work, but there are other cases where the path provides no clear hint).