Testsuite: refactoring only

Authored by thomie.


Testsuite: refactoring only

  • Rename platform_wordsize_qualify to find_expected_file, and make it return a filename instead of an (absolute) filepath.
  • Replace most usages of qualify by in_testdir. Others usage sites will be deleted in a later commit.

These changes will be useful in a later commit, when we'll distinguish
between files in the source directory and those in a (newly created)
test directory.

Reviewed by: austin, bgamari

Differential Revision: https://phabricator.haskell.org/D1186