remove support for the #[start] attribute

tests/ui/array-slice-vec/vec-macro-no-std.rs

@@ -1,21 +1,21 @@
 //@ run-pass
-
 //@ ignore-emscripten no no_std executables
+//@ ignore-wasm different `main` convention
 
-#![feature(lang_items, start, rustc_private)]
 #![no_std]
+#![no_main]
 
+// Import global allocator and panic handler.
 extern crate std as other;
 
-#[macro_use]
-extern crate alloc;
+#[macro_use] extern crate alloc;
 
 use alloc::vec::Vec;
 
 // Issue #16806
 
-#[start]
-fn start(_argc: isize, _argv: *const *const u8) -> isize {
+#[no_mangle]
+extern "C" fn main(_argc: core::ffi::c_int, _argv: *const *const u8) -> core::ffi::c_int {
     let x: Vec<u8> = vec![0, 1, 2];
     match x.last() {
         Some(&2) => (),