Fix remaining clippy warnings (#1340)

* clippy: allow complex encoding function

* clippy: remove unnecessary main() function in doctest

* clippy: remove redundant `Type` suffix on LaneType enum variants

* clippy: ignore incorrect debug_assert_with_mut_call warning

* clippy: fix FDE clippy warnings

cranelift/filetests/src/test_fde.rs

@@ -113,13 +113,13 @@ mod dwarfdump {
 
     impl From<gimli::Error> for Error {
         fn from(err: gimli::Error) -> Self {
-            Error::GimliError(err)
+            Self::GimliError(err)
         }
     }
 
     impl From<fmt::Error> for Error {
         fn from(_: fmt::Error) -> Self {
-            Error::IoError
+            Self::IoError
         }
     }