Link examples to the correct libc when targeting Windows

Author: bjorn3

example/alloc_example.rs

@@ -11,7 +11,8 @@ use alloc_system::System;
 #[global_allocator]
 static ALLOC: System = System;
 
-#[link(name = "c")]
+#[cfg_attr(unix, link(name = "c"))]
+#[cfg_attr(target_env = "msvc", link(name = "msvcrt"))]
 extern "C" {
     fn puts(s: *const u8) -> i32;
 }

example/mini_core.rs

@@ -532,8 +532,8 @@ pub mod intrinsics {
 }
 
 pub mod libc {
-    #[cfg_attr(not(windows), link(name = "c"))]
-    #[cfg_attr(windows, link(name = "msvcrt"))]
+    #[cfg_attr(unix, link(name = "c"))]
+    #[cfg_attr(target_env = "msvc", link(name = "msvcrt"))]
     extern "C" {
         pub fn puts(s: *const i8) -> i32;
         pub fn printf(format: *const i8, ...) -> i32;

example/mod_bench.rs

@@ -1,7 +1,8 @@
 #![feature(start, box_syntax, core_intrinsics, lang_items)]
 #![no_std]
 
-#[link(name = "c")]
+#[cfg_attr(unix, link(name = "c"))]
+#[cfg_attr(target_env = "msvc", link(name = "msvcrt"))]
 extern {}
 
 #[panic_handler]