Mark panic_fmt as no_mangle to work around rust-lang/rust#38281 (#262)

blog/post/03-set-up-rust.md

@@ -57,7 +57,7 @@ Now we place our root source file in `src/lib.rs`:
 pub extern fn rust_main() {}
 
 #[lang = "eh_personality"] extern fn eh_personality() {}
-#[lang = "panic_fmt"] extern fn panic_fmt() -> ! {loop{}}
+#[lang = "panic_fmt"] #[no_mangle] extern fn panic_fmt() -> ! {loop{}}
 ```
 Let's break it down:
 

blog/post/05-allocating-frames.md

@@ -103,6 +103,7 @@ We used `expect` in the code above, which will panic if there is no memory map t
 
 ```rust
 #[lang = "panic_fmt"]
+#[no_mangle]
 extern fn panic_fmt() -> ! {
     println!("PANIC");
     loop{}
@@ -112,6 +113,7 @@ Now we get a `PANIC` message. But we can do even better. The `panic_fmt` functio
 
 ```rust
 #[lang = "panic_fmt"]
+#[no_mangle]
 extern fn panic_fmt(fmt: core::fmt::Arguments, file: &'static str,
     line: u32) -> !
 {

src/lib.rs

@@ -86,6 +86,7 @@ extern "C" fn eh_personality() {}
 
 #[cfg(not(test))]
 #[lang = "panic_fmt"]
+#[no_mangle]
 extern "C" fn panic_fmt(fmt: core::fmt::Arguments, file: &'static str, line: u32) -> ! {
     println!("\n\nPANIC in {} at line {}:", file, line);
     println!("    {}", fmt);