As discussed in Phab:D1187, this approach makes it a bit easier to
inspect the test directory while working on a new test.

The only tests that needed changes are the ones that refer to files in
ancestor directories. Those files are now copied directly into the test
directory.

validate still runs the tests in a temporary directory in /tmp, see
`Note [Running tests in /tmp]` in testsuite/driver/runtests.py.

Update submodule hpc.

Reviewed by: simonmar

Differential Revision: https://phabricator.haskell.org/D2333

GHC Trac Issues: #11980