Remove fold_strip_sign_ops

This patch deletes fold_strip_sign_ops in favour of the
gimple-ssa-backprop.c pass.

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

gcc/
	* fold-const.h (fold_strip_sign_ops): Delete.
	* fold-const.c (fold_strip_sign_ops): Likewise.
	(fold_unary_loc, fold_binary_loc): Remove calls to it.
	* builtins.c (fold_builtin_cos, fold_builtin_cosh)
	(fold_builtin_ccos): Delete.
	(fold_builtin_pow): Don't call fold_strip_sign_ops.
	(fold_builtin_hypot, fold_builtin_copysign): Likewise.
	Remove fndecl argument.
	(fold_builtin_1): Update calls accordingly.  Handle constant
	cos, cosh, ccos and ccosh here.

gcc/testsuite/
	* gcc.dg/torture/builtin-symmetric-1.c: Don't run at -O0.

From-SVN: r229140