cmd/cgo, cmd/compile, cmd/link: remove old style build tags

[Roll-forward of CL 436915 by Tobias Klauser, with builtin and gen
directories dropped now that they've been handled separately.]

The minimum bootstrap version for Go ≥ 1.20 is Go 1.17. That version
supports the new style //go:build lines. Thus the old style //+build
lines can be dropped in this part of the tree as well. Leave the
//+build lines in cmd/dist which will ensure the minimum Go version
during bootstrap.

As suggested by Cherry during review of CL 430496

For #44505

Change-Id: Ifa686656c3e50bf7f92f70747b44d74a7d51bad8
Reviewed-on: https://go-review.googlesource.com/c/go/+/435473
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/cmd/cgo/ast_go1.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build compiler_bootstrap
-// +build compiler_bootstrap
 
 package main
 

src/cmd/cgo/ast_go118.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !compiler_bootstrap
-// +build !compiler_bootstrap
 
 package main
 

src/cmd/compile/internal/base/bootstrap_false.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !compiler_bootstrap
-// +build !compiler_bootstrap
 
 package base
 

src/cmd/compile/internal/base/bootstrap_true.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build compiler_bootstrap
-// +build compiler_bootstrap
 
 package base
 

src/cmd/compile/internal/base/mapfile_mmap.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || (solaris && go1.20)
-// +build darwin dragonfly freebsd linux netbsd openbsd solaris,go1.20
 
 package base
 

src/cmd/compile/internal/base/mapfile_read.go

@@ -3,13 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !(solaris && go1.20)
-// +build !darwin
-// +build !dragonfly
-// +build !freebsd
-// +build !linux
-// +build !netbsd
-// +build !openbsd
-// +build !solaris !go1.20
 
 package base
 

src/cmd/compile/internal/ir/mknode.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build ignore
-// +build ignore
 
 // Note: this program must be run in this directory.
 //   go run mknode.go

src/cmd/compile/internal/ssa/flags_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build amd64 || arm64
-// +build amd64 arm64
 
 package ssa
 

src/cmd/compile/internal/typecheck/_builtin/runtime.go

@@ -7,7 +7,6 @@
 // to avoid depending on having a working compiler binary.
 
 //go:build ignore
-// +build ignore
 
 package runtime
 

src/cmd/compile/internal/typecheck/mkbuiltin.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build ignore
-// +build ignore
 
 // Generate builtin.go from builtin/runtime.go.
 

src/cmd/compile/internal/types2/example_test.go

@@ -6,7 +6,6 @@
 // access to compiled packages for import.
 //
 //go:build !arm && !arm64
-// +build !arm,!arm64
 
 package types2_test
 

src/cmd/internal/bio/buf_mmap.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || (solaris && go1.20)
-// +build darwin dragonfly freebsd linux netbsd openbsd solaris,go1.20
 
 package bio
 

src/cmd/internal/bio/buf_nommap.go

@@ -3,13 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !(solaris && go1.20)
-// +build !darwin
-// +build !dragonfly
-// +build !freebsd
-// +build !linux
-// +build !netbsd
-// +build !openbsd
-// +build !solaris !go1.20
 
 package bio
 

src/cmd/link/elf_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build dragonfly || freebsd || linux || netbsd || openbsd
-// +build dragonfly freebsd linux netbsd openbsd
 
 package main
 

src/cmd/link/internal/ld/outbuf_mmap.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || (solaris && go1.20)
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris,go1.20
 
 package ld
 

src/cmd/link/internal/ld/outbuf_nofallocate.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !darwin && !linux
-// +build !darwin,!linux
 
 package ld
 

src/cmd/link/internal/ld/outbuf_nommap.go

@@ -3,15 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !aix && !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !(solaris && go1.20) && !windows
-// +build !aix
-// +build !darwin
-// +build !dragonfly
-// +build !freebsd
-// +build !linux
-// +build !netbsd
-// +build !openbsd
-// +build !solaris !go1.20
-// +build !windows
 
 package ld