Try to fix some things

* shift so that no panics are generated (otherwise results in linker error)
* no_std as insurance to not get into issues with errors like "cannot satisfy dependencies so `rustc_i128` only shows up once" (pure guessing here, but it doesn't hurt...)

src/libcompiler_builtins/lib.rs

@@ -74,7 +74,7 @@ pub mod reimpls {
         ($a: expr, $b: expr, $ty:ty) => {{
             let (a, b) = ($a, $b);
             let bits = (::core::mem::size_of::<$ty>() * 8) as $ty;
-            let half_bits = bits / 2;
+            let half_bits = bits >> 1;
             if b & half_bits != 0 {
                 <$ty>::from_parts((a.high() >> (b - half_bits)) as <$ty as LargeInt>::LowHalf,
                                   a.high() >> (half_bits - 1))
@@ -97,7 +97,7 @@ pub mod reimpls {
         ($a: expr, $b: expr, $ty:ty) => {{
             let (a, b) = ($a, $b);
             let bits = (::core::mem::size_of::<$ty>() * 8) as $ty;
-            let half_bits = bits / 2;
+            let half_bits = bits >> 1;
             if b & half_bits != 0 {
                 <$ty>::from_parts(a.high() >> (b - half_bits), 0)
             } else if b == 0 {

src/librustc_i128/lib.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 #![allow(non_camel_case_types)]
 #![cfg_attr(not(stage0), feature(i128_type))]
+#![no_std]
 #![crate_type="rlib"]
 #![crate_name="rustc_i128"]