* fold-const.c (fold_strip_sign_ops): Handle copysign.

testsuite:
	* gcc.dg/builtins-20.c: Add cases for copysign.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@118975 138bc75d-0d04-0410-961f-82ee72b054a4