Pass -Wmissing-home-modules to all component types

[hvr]

i.e. not only library components, but also executables, tests and benchmarks.

(With GHC-8.2.1 snapshot 8.2.0.20170521 or earlier, this emits a harmless warning about Main;
the next upcoming snapshot build of GHC-8.2.1 will already omit the spurious warning)

This addresses the other half of #4528

[mention-bot]

@hvr, thanks for your PR! By analyzing the history of the files in this pull request, we identified @luite, @ezyang and @dcoutts to be potential reviewers.

[hvr]

The PPA snapshot ghc-8.2.1_8.2.0.20170522+git.0.c0b82c3 which includes the upstream fix ghc/ghc@72eade6 is already building; give it about 2-3 hours to become available to Travis.

/cc @23Skidoo

[23Skidoo]

Travis is green. Do we need a test case?

[hvr]

@23Skidoo Well, at some point yes; I can think of a couple of constellations we could make into a testcase. However, This is all blocked on #4529 ...

So I'd just merge this one, and maybe create a reminder ticket to write testcases after GHC 8.2.1 got added to the test-matrix.

[23Skidoo]

Merged, thanks!

[23Skidoo]

Also cherry-picked into 2.0.