Canonicalize argument order for commutative functions

Canonicalize argument order for commutative functions

This patch uses information about internal functions to canonicalize
the argument order of calls.

gcc/
	* gimple-fold.c: Include internal-fn.h.
	(fold_stmt_1): If a function maps to an internal one, use
	first_commutative_argument to canonicalize the order of
	commutative arguments.
	* gimple-match-head.c (gimple_resimplify2, gimple_resimplify3)
	(gimple_resimplify4, gimple_resimplify5): Extend commutativity
	checks to functions.

gcc/testsuite/
	* gcc.dg/fmax-fmin-1.c: New test.