Make build.rs exhaustive

build.rs

@@ -1,19 +1,24 @@
 extern crate target_build_utils;
 use target_build_utils::TargetInfo;
+use std::io::Write;
 
 fn main(){
     let target = TargetInfo::new().expect("could not get target info");
     match target.target_os() {
         "linux" | "android" => println!("cargo:rustc-link-lib=dl"),
         "freebsd" | "dragonfly" => println!("cargo:rustc-link-lib=c"),
-
         // netbsd claims dl* will be available to any dynamically linked binary, but I haven’t
         // found any libraries that have to be linked to on other platforms.
-        // "openbsd" | "bitrig" | "netbsd" | "macos" | "ios" => {}
-        //
+        // What happens if the executable is not linked up dynamically?
+        "openbsd" | "bitrig" | "netbsd" | "macos" | "ios" => {}
         // dependencies come with winapi
-        // "windows" => {}
-        _ => {}
+        "windows" => {}
+        tos => {
+            writeln!(::std::io::stderr(),
+                     "Building for an unknown target_os=`{}`!\nPlease report an issue ",
+                     tos).expect("could not report the error");
+            ::std::process::exit(0xfc);
+        }
     }
 
 }