x86: Pass a copy of the string length to cmpstrnqi

x86: Pass a copy of the string length to cmpstrnqi

cmpstrnsi expander may pass the actual string length directly to cmpstrnqi
patterns.  For cmpstrnsi, one of the strings must be a constant and
expand_builtin_strncmp rewrites the length argument to be the minimum of
the const string length and the actual string length.  But it is not the
case for cmpmemsi.  Pass a copy of the string length to cmpstrnqi patterns
to avoid changing the actual string length by cmpstrnqi patterns.

gcc/

	PR target/95443
	* config/i386/i386.md (cmpstrnsi): Pass a copy of the string
	length to cmpstrnqi patterns.

gcc/testsuite/

	PR target/95443
	* gcc.target/i386/pr95443-1.c: New test.
	* gcc.target/i386/pr95443-2.c: Likewise.