rustc: Use 16bit c_int for msp430

Fix regression from c2fe69b9, where main() signature was changed from
using 16bit isize to 32bit c_int for argc parameter/result.

src/librustc_back/target/msp430_none_elf.rs

@@ -16,7 +16,7 @@ pub fn target() -> TargetResult {
         llvm_target: "msp430-none-elf".to_string(),
         target_endian: "little".to_string(),
         target_pointer_width: "16".to_string(),
-        target_c_int_width: "32".to_string(),
+        target_c_int_width: "16".to_string(),
         data_layout: "e-m:e-p:16:16-i32:16-i64:16-f32:16-f64:16-a:8-n8:16-S16".to_string(),
         arch: "msp430".to_string(),
         target_os: "none".to_string(),

src/test/codegen/abi-main-signature-16bit-c-int.rs

@@ -0,0 +1,32 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Checks the signature of the implicitly generated native main()
+// entry point. It must match C's `int main(int, char **)`.
+
+// This test is for targets with 16bit c_int only.
+// ignore-aarch64
+// ignore-arm
+// ignore-asmjs
+// ignore-hexagon
+// ignore-mips
+// ignore-powerpc
+// ignore-powerpc64
+// ignore-s390x
+// ignore-sparc
+// ignore-wasm32
+// ignore-x86
+// ignore-x86_64
+// ignore-xcore
+
+fn main() {
+}
+
+// CHECK: define i16 @main(i16, i8**)

src/test/codegen/abi-main-signature-32bit-c-int.rs

@@ -11,6 +11,9 @@
 // Checks the signature of the implicitly generated native main()
 // entry point. It must match C's `int main(int, char **)`.
 
+// This test is for targets with 32bit c_int only.
+// ignore-msp430
+
 fn main() {
 }