cw: don't shadow pure pre-processing

*** 1469,1479 ****
          default:
                  (void) fprintf(stderr,
                      "Incompatible -xarch= and/or -m32/-m64 options used.\n");
                  exit(2);
          }
!         if (op == CW_O_LINK && (ctx->i_flags & CW_F_SHADOW))
                  exit(0);
  
          if (model && !pic)
                  newae(ctx->i_ae, model);
          if (!nolibc)
--- 1469,1481 ----
          default:
                  (void) fprintf(stderr,
                      "Incompatible -xarch= and/or -m32/-m64 options used.\n");
                  exit(2);
          }
! 
!         if ((op == CW_O_LINK || op == CW_O_PREPROCESS) &&
!             (ctx->i_flags & CW_F_SHADOW))
                  exit(0);
  
          if (model && !pic)
                  newae(ctx->i_ae, model);
          if (!nolibc)