iface: Store flags in interface files
When reporting the reason why a module is recompiled (using
-dump-hi-diffs
), it is much more informative to inform the user about
which flag exactly has changed, rather than just an opaque reference to
a hash.
Now, when there is a difference the precise part of the flags is reported:
codegen flags changed:
before: [Opt_NoTypeableBinds, Opt_OmitYields]
after: [Opt_NoTypeableBinds, Opt_OmitYields, Opt_DictsStrict]
Fixes #25571