Panic handler removal does not work

[jonas-schievink]

trim_panic_handler checks for a section containing the string cortex_m_asm_panic, but we never set that string anywhere.

I guess I meant to put #[link_section] on this function, but never did?

cortex-m/asm/lib.rs

Lines 123 to 139 in fd6a9db

	/// We *must* define a panic handler here, even though nothing here should ever be able to panic.
	///
	/// We prove that nothing will ever panic by calling a function that doesn't exist. If the panic
	/// handler gets linked in, this causes a linker error. We always build this file with optimizations
	/// enabled, but even without them the panic handler should never be linked in.
	#[panic_handler]
	fn panic(_: &core::panic::PanicInfo) -> ! {
	extern "C" {
	#[link_name = "cortex-m internal error: panic handler not optimized out, please file an \
	issue at https://github.com/rust-embedded/cortex-m"]
	fn __cortex_m_should_not_panic() -> !;
	}
	unsafe {
	__cortex_m_should_not_panic();
	}
	}