x86: Change CTZ_DEFINED_VALUE_AT_ZERO to return 0/2

x86: Change CTZ_DEFINED_VALUE_AT_ZERO to return 0/2

Change CTZ_DEFINED_VALUE_AT_ZERO/CTZ_DEFINED_VALUE_AT_ZERO to return 0/2
to enable table-based clz/ctz optimization:

 -- Macro: CLZ_DEFINED_VALUE_AT_ZERO (MODE, VALUE)
 -- Macro: CTZ_DEFINED_VALUE_AT_ZERO (MODE, VALUE)
     A C expression that indicates whether the architecture defines a
     value for 'clz' or 'ctz' with a zero operand.  A result of '0'
     indicates the value is undefined.  If the value is defined for only
     the RTL expression, the macro should evaluate to '1'; if the value
     applies also to the corresponding optab entry (which is normally
     the case if it expands directly into the corresponding RTL), then
     the macro should evaluate to '2'.  In the cases where the value is
     defined, VALUE should be set to this value.

gcc/

	PR target/95863
	* config/i386/i386.h (CTZ_DEFINED_VALUE_AT_ZERO): Return 0/2.
	(CLZ_DEFINED_VALUE_AT_ZERO): Likewise.

gcc/testsuite/

	PR target/95863
	* gcc.target/i386/pr95863-1.c: New test.
	* gcc.target/i386/pr95863-2.c: Likewise.