Replace assert! with debug_assert! in production code paths.

This allows the assertions to be disabled in release builds, so that
the code is faster and smaller, at the expense of not performing the
checks. Assertions can be re-enabled in release builds with the
debug-assertions flag in Cargo.toml, as the top-level Cargo.toml
file does.

lib/cretonne/src/binemit/mod.rs

@@ -110,7 +110,7 @@ where
     let mut divert = RegDiversions::new();
     for ebb in func.layout.ebbs() {
         divert.clear();
-        assert_eq!(func.offsets[ebb], sink.offset());
+        debug_assert_eq!(func.offsets[ebb], sink.offset());
         for inst in func.layout.ebb_insts(ebb) {
             emit_inst(func, inst, &mut divert, sink);
         }