Improve rtx insn vec output

print_rtl will dump the rtx_insn from current until LAST.  But it is only
useful to see the particular insn that called by print_rtx_insn_vec,
Let's call print_rtl_single to display that insn in the gcse and store-motion
pass dump.

2021-04-07  Xionghu Luo  <luoxhu@linux.ibm.com>

gcc/ChangeLog:

	* fold-const.c (fold_single_bit_test): Fix typo.
	* print-rtl.c (print_rtx_insn_vec): Call print_rtl_single
	instead.