Cleanup test framework string formatting

* Use format strings instead of string concatenation.
* Wrap `config.compiler`, `config.hpc` etc. in quotes in `mk/test.mk`, so we
  don't have to in .T scripts and driver/testlib.py.

Update hpc submodule (test cleanup)

Reviewers: austin

Differential Revision: https://phabricator.haskell.org/D718

1 files changed, 0 insertions, 0 deletions

diff --git a/libraries/hpc b/libraries/hpc
-Subproject a071321d33188fb958f42e36778464617c56cfb
+Subproject 08afa91988b68315a035df4702b84b69ba8e125