Port rand to CloudABI.

Cargo.toml

@@ -31,5 +31,8 @@ winapi = { version = "0.3", features = ["minwindef", "ntsecapi", "profileapi", "
 [workspace]
 members = ["rand-derive"]
 
+[target.'cfg(target_os = "cloudabi")'.dependencies]
+cloudabi = "0.0.3"
+
 [target.'cfg(target_os = "fuchsia")'.dependencies]
 fuchsia-zircon = "0.3.2"

src/os.rs

@@ -115,10 +115,12 @@ impl<R: Read> ReadRng<R> {
     }
 }
 
-#[cfg(all(unix, not(target_os = "ios"),
-          not(target_os = "nacl"),
+#[cfg(all(unix,
+          not(target_os = "cloudabi"),
           not(target_os = "freebsd"),
           not(target_os = "fuchsia"),
+          not(target_os = "ios"),
+          not(target_os = "nacl"),
           not(target_os = "openbsd"),
           not(target_os = "redox")))]
 mod imp {
@@ -267,6 +269,33 @@ mod imp {
     }
 }
 
+#[cfg(target_os = "cloudabi")]
+mod imp {
+    extern crate cloudabi;
+
+    use {Error, ErrorKind};
+
+    #[derive(Debug)]
+    pub struct OsRng;
+
+    impl OsRng {
+        pub fn new() -> Result<OsRng, Error> {
+            Ok(OsRng)
+        }
+
+        pub fn try_fill_bytes(&mut self, v: &mut [u8]) -> Result<(), Error> {
+            if unsafe { cloudabi::random_get(v) } == cloudabi::errno::SUCCESS {
+                Ok(())
+            } else {
+                Err(Error::new(
+                    ErrorKind::Unavailable,
+                    "random_get() system call failed",
+                ))
+            }
+        }
+    }
+}
+
 #[cfg(target_os = "ios")]
 mod imp {
     extern crate libc;