Enable and fix several more clippy lints.

lib/codegen/src/context.rs

@@ -52,7 +52,7 @@ impl Context {
     /// The returned instance should be reused for compiling multiple functions in order to avoid
     /// needless allocator thrashing.
     pub fn new() -> Self {
-        Context::for_function(Function::new())
+        Self::for_function(Function::new())
     }
 
     /// Allocate a new compilation context with an existing Function.
@@ -61,7 +61,7 @@ impl Context {
     /// needless allocator thrashing.
     pub fn for_function(func: Function) -> Self {
         Self {
-            func: func,
+            func,
             cfg: ControlFlowGraph::new(),
             domtree: DominatorTree::new(),
             regalloc: regalloc::Context::new(),