os/exec: not add a suffix to Cmd.Path

For avoid data race for cmd.Path , in CL 527820 fixed data race , but addition of suffixe as shown in golang#66586 was also introduced.
The result of call lookExtensions is actually the name passed to os.StartProcess,
But solutions at the time chose to reuse cmd.Path to represent the name passed to os.StartProcess,since this results in golang#66586,
So use new field save call lookExtensions result.

Fixes golang#66586

Change-Id: Ib1baa6d7803f9471af6e38bcb55f0298422e6743

src/os/exec/exec.go

@@ -332,6 +332,10 @@ type Cmd struct {
 	// See https://go.dev/blog/path-security
 	// and https://go.dev/issue/43724 for more context.
 	lookPathErr error
+
+	// cacheLookExtensions cache the result of calling lookExtensions,
+	// use it only on windows.
+	cacheLookExtensions string
 }
 
 // A ctxResult reports the result of watching the Context associated with a
@@ -437,9 +441,7 @@ func Command(name string, arg ...string) *Cmd {
 		// cmd.Dir may be set after we return from this function and that may cause
 		// the command to resolve to a different extension.
 		lp, err := lookExtensions(name, "")
-		if lp != "" {
-			cmd.Path = lp
-		}
+		cmd.cacheLookExtensions = lp
 		if err != nil {
 			cmd.Err = err
 		}
@@ -640,8 +642,8 @@ func (c *Cmd) Start() error {
 		}
 		return c.Err
 	}
-	lp := c.Path
-	if runtime.GOOS == "windows" && !filepath.IsAbs(c.Path) {
+	lp := c.cacheLookExtensions
+	if lp == "" && runtime.GOOS == "windows" {
 		// If c.Path is relative, we had to wait until now
 		// to resolve it in case c.Dir was changed.
 		// (If it is absolute, we already resolved its extension in Command