Add test for extern "C" main function

tests/data/extern-c-main.rs

@@ -0,0 +1,29 @@
+#!/usr/bin/env rust-script
+//! ```cargo
+//! [dependencies]
+//! libc = { version = "0.2", default-features = false }
+//!
+//! [profile.release]
+//! strip = true
+//! lto = true
+//! opt-level = "s" # "z"
+//! codegen-units = 1
+//! panic = "abort"
+//! ```
+
+#![no_std]
+#![no_main]
+
+#[panic_handler]
+fn my_panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[no_mangle]
+pub extern "C" fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    unsafe {
+        libc::printf("--output--\n\0".as_ptr() as *const _);
+        libc::printf("hello, world\n\0".as_ptr() as *const _);
+    }
+    0
+}

tests/tests/script.rs

@@ -260,3 +260,12 @@ fn test_same_flags() {
     )
     .unwrap()
 }
+
+#[test]
+fn test_extern_c_main() {
+    let out = rust_script!("tests/data/extern-c-main.rs").unwrap();
+    scan!(out.stdout_output();
+        ("hello, world") => ()
+    )
+    .unwrap()
+}