e.g.

[3 of 5] Compiling C                (C.hs, C.o)
[4 of 5] Compiling D                (D.hs, D.o) [C changed]
[5 of 5] Compiling E                (E.hs, E.o) [D changed]

The main motivation for this is so that we can give the user a clue
when something is being recompiled because the flags changed:

[1 of 1] Compiling Test2            ( Test2.hs, Test2.o ) [flags changed]