Initial changes to skip libc for cpu time on windows

Mark more non-windows as conditional

src/main.rs

@@ -1,12 +1,13 @@
 extern crate atty;
-
 #[macro_use]
 extern crate clap;
 extern crate colored;
 extern crate indicatif;
-extern crate libc;
 extern crate statistical;
 
+#[cfg(not(target_os = "windows"))]
+extern crate libc;
+
 #[cfg(test)]
 #[macro_use]
 extern crate approx;