Check SCALAR_INT_MODE_P in try_const_anchors

Check SCALAR_INT_MODE_P in try_const_anchors

The const_anchor in cse.cc supports integer constants only.
There is a "gcc_assert (SCALAR_INT_MODE_P (mode))" in
try_const_anchors.

In the latest code, some non-integer modes are used with const int.
For examples:
"set (mem/c:BLK (xx) (const_int 0 [0])" occur in md files of
rs6000, i386, arm, and pa. For this, the mode may be BLKmode.
Pattern "(set (strict_low_part (xx)) (const_int xx))" could
be generated in a few ports. For this, the mode may be VOIDmode.

So, avoid mode other than SCALAR_INT_MODE in try_const_anchors
would be needed.

Some discussions in the previous thread:
https://gcc.gnu.org/pipermail/gcc-patches/2023-June/621097.html

gcc/ChangeLog:

	* cse.cc (try_const_anchors): Check SCALAR_INT_MODE.