* builtins.c (fold_builtin_cbrt, fold_builtin_pow): Rearrange
	code.  Add more cbrt transformations.

testsuite:
	* gcc.dg/builtins-10.c: Reactivate disabled test.
	* gcc.dg/torture/builtin-power-1.c: Likewise.  Also add tests for
	new cbrt transformations.

From-SVN: r96206