env: get GOROOT from env variable or go env GOROOT

compiler/internal/build/build.go

@@ -135,7 +135,7 @@ func Do(args []string, conf *Config) ([]Package, error) {
 		cfg.Overlay = make(map[string][]byte)
 		for file, src := range overlayFiles {
 			overlay := unsafe.Slice(unsafe.StringData(src), len(src))
-			cfg.Overlay[filepath.Join(runtime.GOROOT(), "src", file)] = overlay
+			cfg.Overlay[filepath.Join(env.GOROOT(), "src", file)] = overlay
 		}
 	}
 

compiler/internal/env/env.go

@@ -1,7 +1,9 @@
 package env
 
 import (
+	"bytes"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"strings"
 )
@@ -12,6 +14,21 @@ const (
 	LLGoRuntimePkg     = LLGoCompilerPkg + "/" + LLGoRuntimePkgName
 )
 
+func GOROOT() string {
+	root := os.Getenv("GOROOT")
+	if root != "" {
+		return root
+	}
+	cmd := exec.Command("go", "env", "GOROOT")
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	err := cmd.Run()
+	if err == nil {
+		return strings.TrimSpace(out.String())
+	}
+	panic("cannot get GOROOT: " + err.Error())
+}
+
 func LLGoRuntimeDir() string {
 	root := LLGoROOT()
 	if root != "" {