auto merge of #14963 : w3ln4/rust/master, r=alexcrichton

The aim of these changes is not working out a generic bi-endianness architectures support but to allow people develop for little endian MIPS machines (issue #7190).

src/libstd/os.rs

@@ -1746,6 +1746,10 @@ mod arch_consts {
     pub static ARCH: &'static str = "mips";
 }
 
+#[cfg(target_arch = "mipsel")]
+mod arch_consts {
+    pub static ARCH: &'static str = "mipsel";
+}
 
 #[cfg(test)]
 mod tests {