libgo: update x/sys/cpu to add all GOARCHes supported by gccgo

CL 237897 added additional GOARCHes supported by gccgo to x/sys/cpu.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/238038

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-925d115397e7ec663f669ee5ac31b6dfccea5724
+d4dade353648eae4a1eaa1acd3e4ce1f7180a913
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/golang.org/x/sys/cpu/byteorder.go

@@ -14,15 +14,20 @@ import (
 func hostByteOrder() binary.ByteOrder {
 	switch runtime.GOARCH {
 	case "386", "amd64", "amd64p32",
+		"alpha",
 		"arm", "arm64",
 		"mipsle", "mips64le", "mips64p32le",
+		"nios2",
 		"ppc64le",
-		"riscv", "riscv64":
+		"riscv", "riscv64",
+		"sh":
 		return binary.LittleEndian
 	case "armbe", "arm64be",
+		"m68k",
 		"mips", "mips64", "mips64p32",
 		"ppc", "ppc64",
 		"s390", "s390x",
+		"shbe",
 		"sparc", "sparc64":
 		return binary.BigEndian
 	}