internal/goroot: using strings.CutPrefix replace strings.HasPrefix and strings.TrimPrefix

Change-Id: I63b2af955e2ada6d20e72c10797576d93bbc7e71
Reviewed-on: https://go-review.googlesource.com/c/go/+/435135
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: cuiweixie

src/internal/goroot/gc.go

@@ -69,8 +69,8 @@ func (gd *gccgoDirs) init() {
 	const prefix = "libraries: ="
 	var dirs []string
 	for _, dirEntry := range dirsEntries {
-		if strings.HasPrefix(dirEntry, prefix) {
-			dirs = filepath.SplitList(strings.TrimPrefix(dirEntry, prefix))
+		if after, found := strings.CutPrefix(dirEntry, prefix); found {
+			dirs = filepath.SplitList(after)
 			break
 		}
 	}