Return bools in GPR registers.

Boolean types are returned in %rax, so regclass_for_abi_type() should
return GPR.

Fixes #179.

lib/cretonne/src/isa/intel/abi.rs

@@ -125,7 +125,11 @@ pub fn legalize_signature(sig: &mut ir::Signature, flags: &shared_settings::Flag
 
 /// 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() || ty.is_bool() {
+        GPR
+    } else {
+        FPR
+    }
 }
 
 /// Get the set of allocatable registers for `func`.