cmd/dist: build exec wrappers during bootstrap

The androidtest.bash script encodes the additional steps to build
Go and run tests on Android. In order to add sharded builders and
trybots, Android needs to fit into the usual make.bash + cmd/dist test
pattern.

This change moves building the exec wrapper into cmd/dist bootstrap.

Do the same for iOS while we're here.

Updates #23824

Change-Id: I58a1b0679c3a6c92fdc7fff464b469641f1fee74
Reviewed-on: https://go-review.googlesource.com/c/163618
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/androidtest.bash

@@ -31,14 +31,11 @@ fi
 export CGO_ENABLED=1
 unset GOBIN
 
-# Do the build first, so we can build go_android_exec and cleaner.
+# Do the build first, so we can build the 'cleaner' binary.
 # Also lets us fail early before the (slow) adb push if the build is broken.
 . ./make.bash --no-banner
 export GOROOT=$(dirname $(pwd))
 export PATH=$GOROOT/bin:$PATH
-GOOS=$GOHOSTOS GOARCH=$GOHOSTARCH go build \
-	-o ../bin/go_android_${GOARCH}_exec \
-	../misc/android/go_android_exec.go
 
 export pkgdir=$(dirname $(go list -f '{{.Target}}' runtime))
 if [ "$pkgdir" = "" ]; then

src/cmd/dist/build.go

@@ -1366,14 +1366,42 @@ func cmdbootstrap() {
 	// Remove go_bootstrap now that we're done.
 	xremove(pathf("%s/go_bootstrap", tooldir))
 
+	// Build the exec wrapper if necessary.
+	if wrapperPath := wrapperPathFor(goos, goarch); wrapperPath != "" {
+		oldcc := os.Getenv("CC")
+		os.Setenv("GOOS", gohostos)
+		os.Setenv("GOARCH", gohostarch)
+		os.Setenv("CC", compilerEnvLookup(defaultcc, gohostos, gohostarch))
+		goCmd(cmdGo, "build", "-o", pathf("%s/go_%s_%s_exec%s", gobin, goos, goarch, exe), wrapperPath)
+		// Restore environment.
+		// TODO(elias.naur): support environment variables in goCmd?
+		os.Setenv("GOOS", goos)
+		os.Setenv("GOARCH", goarch)
+		os.Setenv("CC", oldcc)
+	}
+
 	// Print trailing banner unless instructed otherwise.
 	if !noBanner {
 		banner()
 	}
 }
 
+func wrapperPathFor(goos, goarch string) string {
+	switch {
+	case goos == "android":
+		return pathf("%s/misc/android/go_android_exec.go", goroot)
+	case goos == "darwin" && (goarch == "arm" || goarch == "arm64"):
+		return pathf("%s/misc/ios/go_darwin_arm_exec.go", goroot)
+	}
+	return ""
+}
+
 func goInstall(goBinary string, args ...string) {
-	installCmd := []string{goBinary, "install", "-gcflags=all=" + gogcflags, "-ldflags=all=" + goldflags}
+	goCmd(goBinary, "install", args...)
+}
+
+func goCmd(goBinary string, cmd string, args ...string) {
+	installCmd := []string{goBinary, cmd, "-gcflags=all=" + gogcflags, "-ldflags=all=" + goldflags}
 	if vflag > 0 {
 		installCmd = append(installCmd, "-v")
 	}

src/iostest.bash

@@ -56,14 +56,10 @@ export PATH=$GOROOT/bin:$PATH
 export CGO_ENABLED=1
 export CC_FOR_TARGET=$GOROOT/misc/ios/clangwrap.sh
 
-# Run the build for the host bootstrap, so we can build go_darwin_arm_exec.
+# Run the build for the host bootstrap, so we can build detect.go.
 # Also lets us fail early before the (slow) ios-deploy if the build is broken.
 ./make.bash
 
-GOOS=$GOHOSTOS GOARCH=$GOHOSTARCH go build \
-	-o ../bin/go_darwin_${GOARCH}_exec \
-	../misc/ios/go_darwin_arm_exec.go
-
 if [ "$GOIOS_DEV_ID" = "" ]; then
 	echo "detecting iOS development identity"
 	eval $(GOOS=$GOHOSTOS GOARCH=$GOHOSTARCH go run ../misc/ios/detect.go)