Add enums for condition codes.

The icmp and fmp instructions use different kinds of condition codes because
integers and floating point values behave differently.

Add a CondCode trait implementing shared behavior.

src/libcretonne/lib.rs

@@ -8,6 +8,7 @@
 pub const VERSION: &'static str = env!("CARGO_PKG_VERSION");
 
 pub mod types;
+pub mod condcodes;
 pub mod immediates;
 pub mod entities;
 pub mod instructions;