dont use stdcall on x86_64 where it is not a valid ABI

Author: RalfJung

src/items/functions.md

@@ -194,9 +194,9 @@ called from other programming languages like C:
 // Declares a function with the "C" ABI
 extern "C" fn new_i32() -> i32 { 0 }
 
-// Declares a function with the "stdcall" ABI
+// Declares a function with the "vectorcall" ABI
 # #[cfg(target_arch = "x86_64")]
-extern "stdcall" fn new_i32_stdcall() -> i32 { 0 }
+extern "vectorcall" fn new_i32_vectorcall() -> i32 { 0 }
 ```
 
 Just as with [external block], when the `extern` keyword is used and the `"ABI"`