Scaffolding for defining settings.

Settings can be defined globally or per-ISA. They are available to code through
a generated Settings struct with accessor methods per setting.

src/libcretonne/lib.rs

@@ -13,5 +13,6 @@ pub mod write;
 pub mod cfg;
 pub mod dominator_tree;
 pub mod entity_map;
+pub mod settings;
 
 #[cfg(test)]pub mod test_utils;

src/libcretonne/settings.rs

@@ -0,0 +1,7 @@
+//! Shared settings module.
+//!
+//! This module defines data structures to access the settings defined in the meta language.
+
+// Include code generated by `meta/gen_settings.py`. This file contains a public `Settings` struct
+// with an impl for all of the settings defined in `meta/cretonne/settings.py`.
+include!(concat!(env!("OUT_DIR"), "/settings.rs"));