* builtins.c (fold_builtin): Add new builtin optimizations for
	sqrt and/or cbrt.
	* fold-const.c (fold): Likewise.

testsuite:
	* gcc.dg/torture/builtin-explog-1.c: Add new cases.
	* gcc.dg/torture/builtin-math-1.c: Likewise.
	* builtin-power-1.c: New test.

From-SVN: r79959