Not gnereate binding for variadic function with ms_abi

rustc fail to compile variadic function with ms_abi:
error[E0045]: variadic function must have C or cdecl calling convention

As suggested in issue, this short term fix: not generate binding
and emit a warning.

Fixes rust-lang#1281

Author: jeanphilippeD

src/codegen/mod.rs

@@ -3338,6 +3338,10 @@ impl CodeGenerator for Function {
                 warn!("Skipping function with thiscall ABI that isn't supported by the configured Rust target");
                 return;
             }
+            Abi::Win64 if signature.is_variadic() => {
+                warn!("Skipping variadic function with Win64 ABI that isn't supported");
+                return;
+            }
             Abi::Unknown(unknown_abi) => {
                 panic!(
                     "Invalid or unknown abi {:?} for function {:?} ({:?})",

tests/expectations/tests/abi_variadic_function.rs

@@ -0,0 +1,6 @@
+/* automatically generated by rust-bindgen */
+
+extern "C" {
+    #[link_name = "\u{1}_Z1bcz"]
+    pub fn b(arg1: ::std::os::raw::c_char, ...) -> ::std::os::raw::c_char;
+}

tests/headers/abi_variadic_function.hpp

@@ -0,0 +1,4 @@
+// bindgen-flags: -- -std=c++11
+
+char __attribute__((ms_abi)) a(char, ...);
+char b(char, ...);