Add calloc test

tests/run-pass/calloc.rs

@@ -0,0 +1,26 @@
+//ignore-windows: Uses POSIX APIs
+
+#![feature(rustc_private)]
+
+use core::slice;
+
+extern crate libc;
+
+fn main() {
+    unsafe {
+        let p1 = libc::calloc(0, 0);
+        assert!(p1.is_null());
+
+        let p2 = libc::calloc(20, 0);
+        assert!(p2.is_null());
+
+        let p3 = libc::calloc(0, 20);
+        assert!(p3.is_null());
+
+        let p4 = libc::calloc(4, 8) as *const u8;
+        assert!(!p4.is_null());
+
+        let slice = slice::from_raw_parts(p4, 4 * 8);
+        assert_eq!(&slice, &[0_u8; 4 * 8]);
+    }
+}