Flip vectorization to forced SLP

The following flips the vectorizer to forced SLP, there is almost
no expected fallout at this point, the remains should be target
specific cost modeling issues.

	* params.opt (vect-force-slp): Default to 1.

gcc/params.opt

@@ -1207,7 +1207,7 @@ Common Joined UInteger Var(param_vect_induction_float) Init(1) IntegerRange(0, 1
 Enable loop vectorization of floating point inductions.
 
 -param=vect-force-slp=
-Common Joined UInteger Var(param_vect_force_slp) Init(0) IntegerRange(0, 1) Param Optimization
+Common Joined UInteger Var(param_vect_force_slp) Init(1) IntegerRange(0, 1) Param Optimization
 Force the use of SLP when vectorizing, fail if not possible.
 
 -param=vrp-block-limit=