[committed][RISC-V] Turn on overlap_op_by_pieces for generic-ooo tuning

Per quick email exchange with Palmer.  Given the triviality, I'm just pushing
it.

gcc/
	* config/riscv/riscv.cc (generic_ooo_tune_info): Turn on
	overlap_op_by_pieces.

gcc/config/riscv/riscv.cc

@@ -536,7 +536,7 @@ static const struct riscv_tune_param generic_ooo_tune_info = {
   4,						/* fmv_cost */
   false,					/* slow_unaligned_access */
   false,					/* use_divmod_expansion */
-  false,					/* overlap_op_by_pieces */
+  true,						/* overlap_op_by_pieces */
   RISCV_FUSE_NOTHING,                           /* fusible_ops */
   &generic_vector_cost,				/* vector cost */
 };