default_alloc_error_handler requires the linker to omit __rg_oom from liballoc

[bjorn3]

__rg_oom calls the rust_oom symbol (aka the "oom" weak lang item). This symbol is not defined when using default_alloc_error_handler.

rust/library/alloc/src/alloc.rs

Lines 403 to 412 in 352e621

	// if there is an `#[alloc_error_handler]`
	#[rustc_std_internal_symbol]
	pub unsafe extern "C-unwind" fn __rg_oom(size: usize, align: usize) -> ! {
	let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
	extern "Rust" {
	#[lang = "oom"]
	fn oom_impl(layout: Layout) -> !;
	}
	unsafe { oom_impl(layout) }
	}

This causes https://github.com/rust-lang/rust/blob/31535841701e0bf7ef33998024376f2cedd8b3e3/src/test/ui/allocator/no_std-alloc-error-handler-default.rs to fail with cg_clif as it uses -Zfunction-sections=no by default. I suspect it would also cause it to fail for windows as windows has this default too.

Applying the approach of #86844 to the alloc error handler too should trivially fix this. This PR is still pending decision if it should be done or not.

[bjorn3]

Fixed by #103061.