hopefully deal with _Unwind_Resume symbols

Author: RalfJung

tests/ui/format-no-std.rs

@@ -38,6 +38,17 @@ extern "C" fn rust_eh_personality() {
     loop {}
 }
 
+/// Workaround for rustc bug: https://github.com/rust-lang/rust/issues/47493,
+/// https://github.com/rust-lang/rust/issues/53301.
+///
+/// It shouldn't even be possible to reach this function, thanks to panic=abort,
+/// but liballoc is compiled with unwinding enabled and that ends up making unreachable
+/// references to this.
+#[no_mangle]
+extern "C" fn _Unwind_Resume() -> ! {
+    unreachable!("Unwinding not supported");
+}
+
 #[no_mangle]
 extern "C" fn main(_argc: core::ffi::c_int, _argv: *const *const u8) -> core::ffi::c_int {
     let s = format!("{}", 1_isize);