Reenable tests that previously use Diagnostic verification

[kyleheadley]

PR #488 disables diagnostic verification of 3c's rewriter (and other verification, but we were only using it for the rewriter). 8 tests made use of it and need to be refactored:

  Clang :: 3C/base_subdir/canwrite_constraints.c
  Clang :: 3C/base_subdir/canwrite_constraints_symlink.c
  Clang :: 3C/base_subdir/canwrite_constraints_unimplemented.c
  Clang :: 3C/macro_rewrite_error.c
  Clang :: 3C/root_cause.c
  Clang :: 3C/stdout_mode_write_other.c
  Clang :: 3C/diag_verifier_fail.c
  Clang :: 3C/diag_verifier_pass.c

[mattmccutchen-cci]

macro_function_call.c will also need to be updated to whatever new mechanism we develop: see #519.