Move condcodes.rs to a new crate, cranelift-codegen-shared

This move allows the `IntCC`/`FloatCC` enums to be used in both meta (for predicate matching) and in codegen. To avoid breaking any code dependent on the previous location of condcodes.rs (`cranelift-codegen/src/condcodes.rs`), the module is re-exported under `cranelift_codegen::ir`.

cranelift/codegen/src/ir/mod.rs

@@ -1,7 +1,6 @@
 //! Representation of Cranelift IR functions.
 
 mod builder;
-pub mod condcodes;
 pub mod constant;
 pub mod dfg;
 pub mod entities;
@@ -55,6 +54,7 @@ pub use crate::ir::table::TableData;
 pub use crate::ir::trapcode::TrapCode;
 pub use crate::ir::types::Type;
 pub use crate::ir::valueloc::{ArgumentLoc, ValueLoc};
+pub use cranelift_codegen_shared::condcodes;
 
 use crate::binemit;
 use crate::entity::{entity_impl, PrimaryMap, SecondaryMap};