Match: Refactor the signed SAT_* match for saturated value [NFC]

Match: Refactor the signed SAT_* match for saturated value [NFC]

This patch would like to refactor the all signed SAT_* patterns for
the saturated value.  Aka, overflow to INT_MAX when > 0 and downflow
to INT_MIN when < 0.  Thus, we can remove sorts of duplicated expression
in different patterns.

The below test suites are passed for this patch.
* The rv64gcv fully regression test.
* The x86 bootstrap test.
* The x86 fully regression test.

gcc/ChangeLog:

	* match.pd: Extract saturated value match for signed SAT_*.

Signed-off-by: Pan Li <pan2.li@intel.com>