Make specific ISA sub-modules private.

We don't want ISA-specific details exposed in the public Cretonne APIs.

lib/cretonne/meta/gen_settings.py

@@ -86,6 +86,7 @@ def gen_getters(sgrp, fmt):
     Emit getter functions for all the settings in fmt.
     """
     fmt.doc_comment("User-defined settings.")
+    fmt.line('#[allow(dead_code)]')
     with fmt.indented('impl Flags {', '}'):
         fmt.doc_comment('Get a view of the boolean predicates.')
         with fmt.indented(

lib/cretonne/src/isa/mod.rs

@@ -56,16 +56,16 @@ use isa::enc_tables::Encodings;
 use std::fmt;
 
 #[cfg(build_riscv)]
-pub mod riscv;
+mod riscv;
 
 #[cfg(build_intel)]
-pub mod intel;
+mod intel;
 
 #[cfg(build_arm32)]
-pub mod arm32;
+mod arm32;
 
 #[cfg(build_arm64)]
-pub mod arm64;
+mod arm64;
 
 pub mod registers;
 mod encoding;