`#![windows_subsystem = "windows"]` overwrites entrypoint symbol name

Description

Using #![windows_subsystem = "windows"] overwrites the default entrypoint symbol name WinMainCRTStartup with mainCRTStartup. This is by design, but can be unexpected in certain scenarios, for example when specifying #![no_main]. It should either be adapted for those scenarios, or mentioned in the user facing documentation.

Reproduction

1. Create example.rs:

   #![no_main]
   #![no_std]
   
   #[cfg(not(test))]
   #[panic_handler]
   fn panic(_: &core::panic::PanicInfo) -> ! {
       loop {}
   }
   
   #[unsafe(no_mangle)]
   extern "system" fn WinMainCRTStartup() -> i32 {
       0
   }
   

2. Linking succeeds via: rustc example.rs -C panic=abort -C link-arg=/Subsystem:Windows
3. Add #![windows_subsystem = "windows"] to example.rs
4. Linking fails via: rustc example.rs -C panic=abort

Reproduce the two rustc commands with the provided example.rs, then inspect the linked logic in compiler/rustc_codegen_ssa/src/back/linker.rs and the Windows subsystem attribute documentation in the Rust Reference. Determine whether the behavior should change for no_main or be documented, and consider the issue done when the selected resolution is verified by the reproduction or clearly explained to users.