Add -mwin32 on Windows targets

Author: abonander

src/lib.rs

@@ -1,6 +1,7 @@
 use std::io::Command;
 use std::io::process::InheritFd;
 use std::default::Default;
+use std::borrow::ToOwned;
 
 /// Extra configuration to pass to gcc.
 pub struct Config {
@@ -16,11 +17,17 @@ pub struct Config {
 
 impl Default for Config {
     fn default() -> Config {
+        let mut flags = Vec::new();
+
+        if cfg!(target_os = "windows") {
+            flags.push("-mwin32".to_owned());    
+        }
+
         Config {
             include_directories: Vec::new(),
             definitions: Vec::new(),
             objects: Vec::new(),
-            flags: Vec::new(),
+            flags: flags,
         }
     }
 }