testsuite/gcc.dg/uninit-pred-9_b.c:20: Fix XPASS for various targets

testsuite/gcc.dg/uninit-pred-9_b.c:20: Fix XPASS for various targets

The xfail for "*-*-*" here, set in r14-4089-gd45ddc2c04e471
"tree-optimization/111294 - backwards threader PHI costing"
was somewhat too general and made this test XPASS for a
number of targets.  The common factor for those targets is
that they either explicitly or by default define
LOGICAL_OP_NON_SHORT_CIRCUIT as 0 (see fold-const.cc).

Instead of changing *-*-* to a seemingly random set of
xfailed targets or inventing a new testsuite
effective-target predicate for logical-op-short-circuited
targets or the opposite, let's just force a setting that
removes the need for the xfail for all targets, by
overriding with --param=logical-op-non-short-circuit=0.

	* gcc.dg/uninit-pred-9_b.c: Remove xfail for line 20.  Pass
	--param=logical-op-non-short-circuit=0.  Comment why.