Move sqrt and cbrt simplifications to match.pd

Move sqrt and cbrt simplifications to match.pd

This patch moves the sqrt and cbrt simplification rules to match.pd.
builtins.c now only does the constant folding.

Bootstrapped & regression-tested on x86_64-linux-gnu.

gcc/
	* builtins.c (fold_builtin_sqrt, fold_builtin_cbrt): Delete.
	(fold_builtin_1): Update accordingly.  Handle constant arguments here.
	* match.pd: Add rules previously handled by fold_builtin_sqrt
	and fold_builtin_cbrt.

gcc/testsuite/
	* gcc.dg/builtins-47.c: Test the optimized dump instead.

From-SVN: r228616