hadrian: Rebuild with -B[PATTERNS] runs extra rules

Summary

While using the -B[PATTERN]/--rebuild[=PATTERN] flag with Hadrian, it's not just rules matching the pattern that are rerun, but seemingly all the rules leading up to it too. The Hadrian documentation says that -B[PATTERN] will "Rebuild matching files", so I wouldn't expect it to also rebuild these extra files. Most of these rules run GHC commands that just output compilation IS NOT required.

Steps to reproduce

Build using a particular flavour and flags.

hadrian/build.stack.sh -c -j --flavour=quickest

Rebuild with everything the same, with an added -B [some target], eg:

hadrian/build.stack.sh -c -j --flavour=quickest -B _build/stage0/compiler/build/HsInstances.o

Expected behavior

The rebuild will rerun many unnecessary rules, but will likely complete faster since no actual compilation will be done for most of them.

Environment

• GHC version used: 8.6.5 with Stack