Extend vect_recog_cond_expr_convert_pattern to handle REAL_CST

Extend vect_recog_cond_expr_convert_pattern to handle REAL_CST

REAL_CST is handled if it can be represented in different floating
point types without loss of precision or under fast math.

gcc/ChangeLog:

	PR tree-optimization/103771
	* match.pd (cond_expr_convert_p): Extend the match to handle
	REAL_CST.
	* tree-vect-patterns.cc
	(vect_recog_cond_expr_convert_pattern): Handle REAL_CST.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr103771-5.c: New test.
	* gcc.target/i386/pr103771-6.c: New test.