Fork channel

Create a new channel as a copy of main.

Rename channel

Rename main to:

Delete channel

Delete main? This cannot be undone.

pr21687.cpp
// RUN: rm -rf %t
// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I%S/Inputs/PR21687 -emit-llvm-only %s
#include "c.h"