Update to rustfmt-preview (#348)

* Update to rustfmt-preview.

* Run "cargo fmt --all" with rustfmt 0.4.1.

rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.

* Fix a long line that rustfmt 0.4.1 can't handle.

* Remove unneeded commas left behind by rustfmt.

lib/codegen/src/isa/arm64/abi.rs

@@ -17,7 +17,11 @@ pub fn legalize_signature(
 
 /// Get register class for a type appearing in a legalized signature.
 pub fn regclass_for_abi_type(ty: ir::Type) -> RegClass {
-    if ty.is_int() { GPR } else { FPR }
+    if ty.is_int() {
+        GPR
+    } else {
+        FPR
+    }
 }
 
 /// Get the set of allocatable registers for `func`.