Notes on the SCFI testsuite in GAS:

* At this time, SCFI machinery is only supported for x86_64.

* When adding more tests, please keep CFI annotations updated in the .s files.
  Ideally the test should be run with and without --scfi (as is done currently
  for the core SCFI tests); Such workflow ensures sanity checking of the CFI
  annotations. 

* Note that GAS issues a warning:
    "Warning: --scfi=all ignores some user-specified CFI directive"
  when it encounters CFI directives in the input assembly and --scfi (=all) is
  active.  To bypass the noise from this warning, while keeping the testcases
  useful/understandable, most tests are run twice. E.g.,
     - run_dump_test "scfi-cfi-add-1" // ignores warnings
     - run_list_test "scfi-cfi-add-1" "--scfi --warn" // tests warnings
