llvm-go: Add flag for specifying path to go command.

[axw]

LGTM

tools/llvm-go/llvm-go.go

 #cgo LDFLAGS: %s
 */
 import "C"
 
 type (run_build_sh int)
 `, flags.cpp, flags.cxx, flags.ld)
 }
 
-func runGoWithLLVMEnv(args []string, cc, cxx, llgo, cppflags, cxxflags, ldflags string) {
+func runGoWithLLVMEnv(args []string, cc, cxx, gocmd, llgo, cppflags, cxxflags, ldflags string) {
   args = addTag(args, "byollvm")
 
   srcdir := llvmConfig("--src-root")
 
   tmpgopath, err := ioutil.TempDir("", "gopath")
   if err != nil {
     panic(err.Error())
   }
if !strings.HasPrefix(v, "CC=") &&
       !strings.HasPrefix(v, "CGO_CXXFLAGS=") &&
       !strings.HasPrefix(v, "CGO_LDFLAGS=") &&
       !strings.HasPrefix(v, "GOPATH=") &&
       !strings.HasPrefix(v, "PATH=") {
       newenv = append(newenv, v)
     }
   }
 
-  gocmdpath, err := exec.LookPath("go")
+  gocmdpath, err := exec.LookPath(gocmd)
   if err != nil {
     panic(err.Error())
   }
 
-  proc, err := os.StartProcess(gocmdpath, append([]string{"go"}, args...),
+  proc, err := os.StartProcess(gocmdpath, append([]string{gocmd}, args...),
     &os.ProcAttr{
       Env:   newenv,
       Files: []*os.File{os.Stdin, os.Stdout, os.Stderr},
     })
   if err != nil {
     panic(err.Error())
   }
   ps, err := proc.Wait()

 }
 
 func main() {
   cc := os.Getenv("CC")
   cxx := os.Getenv("CXX")
   cppflags := os.Getenv("CGO_CPPFLAGS")
   cxxflags := os.Getenv("CGO_CXXFLAGS")
   ldflags := os.Getenv("CGO_LDFLAGS")
+  gocmd := "go"
   llgo := ""
 
   args := os.Args[1:]
   DONE: for {
     switch {
     case len(args) == 0:
       usage()
     case strings.HasPrefix(args[0], "cc="):
       cc = args[0][3:]
       args = args[1:]
     case strings.HasPrefix(args[0], "cxx="):
       cxx = args[0][4:]
       args = args[1:]
+    case strings.HasPrefix(args[0], "go="):
+      gocmd = args[0][3:]
+      args = args[1:]
     case strings.HasPrefix(args[0], "llgo="):
       llgo = args[0][5:]
       args = args[1:]
     case strings.HasPrefix(args[0], "cppflags="):
       cppflags = args[0][9:]
       args = args[1:]
     case strings.HasPrefix(args[0], "cxxflags="):
       cxxflags = args[0][9:]
       args = args[1:]
     case strings.HasPrefix(args[0], "ldflags="):
       ldflags = args[0][8:]
       args = args[1:]
     default:
       break DONE
     }
   }
 
   switch args[0] {
   case "build", "get", "install", "run", "test":
-    runGoWithLLVMEnv(args, cc, cxx, llgo, cppflags, cxxflags, ldflags)
+    runGoWithLLVMEnv(args, cc, cxx, gocmd, llgo, cppflags, cxxflags, ldflags)
   case "print-components":
     printComponents()
   case "print-config":
     printConfig()
   default:
     usage()
   }
 }