cse: Check volatile memory in cselib_redundant_set_p

cse: Check volatile memory in cselib_redundant_set_p

For h8300-elf, gcc.dg/pr114768.c fails when compiled with -O2 -msx since
cselib_redundant_set_p returns true when called with

(gdb) call debug (set)
(set (mem:HI (reg/f:SI 0 r0 [orig:21 p ] [21]) [1 *p_3(D)+0 S2 A16])
    (mem/v:HI (reg/f:SI 0 r0 [orig:21 p ] [21]) [1 MEM[(volatile int *)p_3(D)]+0 S2 A16]))
(gdb)

from reload_cse_regs.  Update cselib_redundant_set_p to return false for
volatile memory source or destination.

gcc/

	PR target/122343
	* cselib.cc (cselib_redundant_set_p): Return false for volatile
	memory source or destination.

gcc/testsuite/

	PR target/122343
	* gcc.dg/pr122343-1.c: New test.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>