Vendor in c/image with sigstore support

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/golang.org/x/crypto/sha3/xor.go

@@ -0,0 +1,24 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (!amd64 && !386 && !ppc64le) || purego
+// +build !amd64,!386,!ppc64le purego
+
+package sha3
+
+// A storageBuf is an aligned array of maxRate bytes.
+type storageBuf [maxRate]byte
+
+func (b *storageBuf) asBytes() *[maxRate]byte {
+	return (*[maxRate]byte)(b)
+}
+
+var (
+	xorIn            = xorInGeneric
+	copyOut          = copyOutGeneric
+	xorInUnaligned   = xorInGeneric
+	copyOutUnaligned = copyOutGeneric
+)
+
+const xorImplementationUnaligned = "generic"