Added indexBytePortal from standard library to link as implementation for internal/bytealg.IndexByte

Author: bgould

src/runtime/bytes.go

@@ -0,0 +1,11 @@
+package runtime
+
+//go:linkname indexBytePortable internal/bytealg.IndexByte
+func indexBytePortable(s []byte, c byte) int {
+	for i, b := range s {
+		if b == c {
+			return i
+		}
+	}
+	return -1
+}