Move ldexp, scalbn and scalbln folds to match.pd

Move ldexp, scalbn and scalbln folds to match.pd

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/
	* builtins.c (fold_builtin_load_exponent): Rename to...
	(fold_const_builtin_load_exponent): ...this and only handle
	constant arguments.
	(fold_builtin_2): Update accordingly.
	* match.pd: Add rules previously handled by fold_builtin_load_exponent.

gcc/testsuite/
	* gcc.dg/torture/builtin-ldexp-1.c: Skip at -O9,

From-SVN: r229434