tree-optimization/84201 - add --param vect-induction-float

This adds a --param to allow disabling of vectorization of
floating point inductions.  Ontop of -Ofast this should allow
549.fotonik3d_r to not miscompare.

2022-03-08  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/84201
	* params.opt (-param=vect-induction-float): Add.
	* doc/invoke.texi (vect-induction-float): Document.
	* tree-vect-loop.cc (vectorizable_induction): Honor
	param_vect_induction_float.

	* gcc.dg/vect/pr84201.c: New testcase.