testsuite: Use explicit -ftree-cselim in tests using -fdump-tree-cselim-details

testsuite: Use explicit -ftree-cselim in tests using -fdump-tree-cselim-details

When testing for Nios II (gcc-testresults shows this for various other
targets as well), tests scanning cselim dumps produce an UNRESOLVED
result because those dumps do not exist.

cselim is enabled conditionally by code in toplev.c:

  if (flag_tree_cselim == AUTODETECT_VALUE)
    {
      if (HAVE_conditional_move)
	flag_tree_cselim = 1;
      else
	flag_tree_cselim = 0;
    }

Add explicit -ftree-cselim to dg-options in the affected tests (as
already used by some other tests of cselim dumps) so that this dump
exists on all architectures.

Tested with no regressions with cross to nios2-elf, where this causes
the tests in question to PASS instead of being UNRESOLVED.

	* gcc.dg/tree-ssa/pr89430-1.c, gcc.dg/tree-ssa/pr89430-2.c,
	gcc.dg/tree-ssa/pr89430-3.c, gcc.dg/tree-ssa/pr89430-4.c,
	gcc.dg/tree-ssa/pr89430-5.c, gcc.dg/tree-ssa/pr89430-6.c,
	gcc.dg/tree-ssa/pr89430-7-comp-ref.c,
	gcc.dg/tree-ssa/pr89430-8-mem-ref-size.c: Use -ftree-cselim.

(cherry picked from commit d081516ae1771984bfacb9f2c402a1973fa70d69)