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/shared/src/lib.rs

@@ -0,0 +1,26 @@
+//! This library contains code that is common to both the `cranelift-codegen` and
+//! `cranelift-codegen-meta` libraries.
+
+#![deny(missing_docs, trivial_numeric_casts, unused_extern_crates)]
+#![warn(unused_import_braces)]
+#![cfg_attr(feature = "std", deny(unstable_features))]
+#![cfg_attr(feature = "clippy", plugin(clippy(conf_file = "../../clippy.toml")))]
+#![cfg_attr(feature = "cargo-clippy", allow(clippy::new_without_default))]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    warn(
+        clippy::float_arithmetic,
+        clippy::mut_mut,
+        clippy::nonminimal_bool,
+        clippy::option_map_unwrap_or,
+        clippy::option_map_unwrap_or_else,
+        clippy::print_stdout,
+        clippy::unicode_not_nfc,
+        clippy::use_self
+    )
+)]
+
+pub mod condcodes;
+
+/// Version number of this crate.
+pub const VERSION: &str = env!("CARGO_PKG_VERSION");