Add settings::Configurable and isa to the prelude.

These are useful for API users that customize the TargetIsa.

lib/umbrella/src/lib.rs

@@ -30,6 +30,8 @@ pub mod prelude {
     pub use codegen::ir::types;
     pub use codegen::ir::condcodes::{IntCC, FloatCC};
     pub use codegen::ir::immediates::{Ieee32, Ieee64};
+    pub use codegen::settings::{self, Configurable};
+    pub use codegen::isa;
 
     pub use frontend::{FunctionBuilderContext, FunctionBuilder, Variable};
 }