ci: add nopanic check for windows

[newpavlov]

Relevant issue: #516

[newpavlov]

It looks like link.exe does not perform the same dead code elimination as linkers in Linux and macOS (I confirmed it with an empty getrandom_wrapper function), so we need to reconsider our approach towards nopanic checks on Windows.

[ChrisDenton]

On my machine link.exe does eliminate it but still wants it to exist in the first place. In any case, you could use lto to eliminate the symbol before the linker even sees it.

[newpavlov]

LTO is irrelevant here. I tried to use the following program:

#![no_std]

#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
    extern "C" {
        fn panic_nonexistent() -> !;
    }
    unsafe { panic_nonexistent() }
}

#[no_mangle]
pub extern "C" fn getrandom_wrapper(_: *mut u8, _: usize) -> u32 {
    0
}

And it still was failing the linking step. I will try to use a slightly different approach to this a bit later.

[ChrisDenton]

It should be highly relevant. Link time optimization happens before the linker is given anything (unless you use llvm's linker) so if panic is never called then no references to panic_nonexistent will exist by the time the linker sees it.

[newpavlov]

Huh, you are right. Thank you! TIL, before that I thought LTO applies only during "link time" and has not effect in cases like the snippet above.