Fix and add tests for %MEM-REF and %MEM-SET evaluation order.

- Some minor reformatting of LOOP forms to pacify cl-indent.
- Add new regression tests to check the evaluation order of
  %MEM-REF and %MEM-SET.
- Add the necessary ONCE-ONLY forms to the compiler macros.
- Have the CFFI-TESTS package use CFFI-SYS for testing primitives.