internal/cpu: make architectures without initialization work explicit

When cpu_no_init.go was created most architectures did not have
code in the doinit function. Currently only mips(le), riscv64 and
wasm do not have empty doinit functions.

Keeping cpu_no_init.go around does not reduce the work to satisfy
the build process when adding support for new architectures.

To support a new architecture a new file or build directive has to
be added to an existing file at any rate to define the constant
CacheLinePadSize. A new empty doinit can then be created in the
new file or the existing doinit can be reused when adding the
additional build directive.

Change-Id: I58a97f8cdf1cf1be85c37f4550c40750358aa031
Reviewed-on: https://go-review.googlesource.com/c/go/+/263801
Trust: Martin Möhrmann <moehrmann@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

src/internal/cpu/cpu_mips.go

@@ -5,3 +5,6 @@
 package cpu
 
 const CacheLinePadSize = 32
+
+func doinit() {
+}

src/internal/cpu/cpu_mipsle.go

@@ -5,3 +5,6 @@
 package cpu
 
 const CacheLinePadSize = 32
+
+func doinit() {
+}

src/internal/cpu/cpu_no_init.go

@@ -1,18 +0,0 @@
-// Copyright 2018 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.
-
-// +build !386
-// +build !amd64
-// +build !arm
-// +build !arm64
-// +build !ppc64
-// +build !ppc64le
-// +build !s390x
-// +build !mips64
-// +build !mips64le
-
-package cpu
-
-func doinit() {
-}

src/internal/cpu/cpu_riscv64.go

@@ -5,3 +5,6 @@
 package cpu
 
 const CacheLinePadSize = 32
+
+func doinit() {
+}

src/internal/cpu/cpu_wasm.go

@@ -5,3 +5,6 @@
 package cpu
 
 const CacheLinePadSize = 64
+
+func doinit() {
+}