cmd/go: use local state object in bug.runBug

This commit modifies `bug.runBug` to construct a new modload.State
object using the new constructor instead of the current global
`modload.LoaderState` variable.

This commit is part of the overall effort to eliminate global
modloader state.

[git-generate]
cd src/cmd/go/internal/bug
rf '
  add bug.go:/func runBug\(/-0 var moduleLoaderState *modload.State
  ex {
    import "cmd/go/internal/modload";
    modload.LoaderState -> moduleLoaderState
  }
  add runBug://+0 moduleLoaderState := modload.NewState()
  rm bug.go:/var moduleLoaderState \*modload.State/
'

Change-Id: Ic4f74d2127f667491136ee4bad4388b4d606821e
Reviewed-on: https://go-review.googlesource.com/c/go/+/711123
Reviewed-by: Michael Matloob <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>

Author: jitsu-net

src/cmd/go/internal/bug/bug.go

@@ -42,16 +42,17 @@ func init() {
 }
 
 func runBug(ctx context.Context, cmd *base.Command, args []string) {
+	moduleLoaderState := modload.NewState()
 	if len(args) > 0 {
 		base.Fatalf("go: bug takes no arguments")
 	}
-	work.BuildInit(modload.LoaderState)
+	work.BuildInit(moduleLoaderState)
 
 	var buf strings.Builder
 	buf.WriteString(bugHeader)
 	printGoVersion(&buf)
 	buf.WriteString("### Does this issue reproduce with the latest release?\n\n\n")
-	printEnvDetails(modload.LoaderState, &buf)
+	printEnvDetails(moduleLoaderState, &buf)
 	buf.WriteString(bugFooter)
 
 	body := buf.String()