vendor: Move back to upstream KCP (fixes #4407)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4614

vendor/github.com/klauspost/reedsolomon/galois_noasm.go

@@ -0,0 +1,27 @@
+//+build !amd64 noasm appengine
+//+build !arm64 noasm appengine
+
+// Copyright 2015, Klaus Post, see LICENSE for details.
+
+package reedsolomon
+
+func galMulSlice(c byte, in, out []byte, ssse3, avx2 bool) {
+	mt := mulTable[c]
+	for n, input := range in {
+		out[n] = mt[input]
+	}
+}
+
+func galMulSliceXor(c byte, in, out []byte, ssse3, avx2 bool) {
+	mt := mulTable[c]
+	for n, input := range in {
+		out[n] ^= mt[input]
+	}
+}
+
+// slice galois add
+func sliceXor(in, out []byte, sse2 bool) {
+	for n, input := range in {
+		out[n] ^= input
+	}
+}