ISLE: fix compile fuzz target, and fix a simple error-reporting bug. (#3845)

It seems our `compile` fuzz target for ISLE has not been regularly
tested, as it was never updated for the `isle` -> `cranelift_isle` crate
renaming. This PR fixes it to compile again.

This also includes a simple fix in the typechecking: when verifying that
a term decl is valid, we might insert a term ID into the name->ID map
before fully checking that all of the types exist, and then skipping
(for error recovery purposes) the actual push onto the term-signature
vector if one of the types does have an error. This phantom TID can
later cause a panic. The fix is to avoid adding to the map until we have
fully verified the term decl.

cranelift/isle/fuzz/fuzz_targets/compile.rs

@@ -5,21 +5,21 @@ use libfuzzer_sys::fuzz_target;
 fuzz_target!(|s: &str| {
     let _ = env_logger::try_init();
 
-    let lexer = isle::lexer::Lexer::from_str(s, "fuzz-input.isle");
+    let lexer = cranelift_isle::lexer::Lexer::from_str(s, "fuzz-input.isle");
     log::debug!("lexer = {:?}", lexer);
     let lexer = match lexer {
         Ok(l) => l,
         Err(_) => return,
     };
 
-    let defs = isle::parser::parse(lexer);
+    let defs = cranelift_isle::parser::parse(lexer);
     log::debug!("defs = {:?}", defs);
     let defs = match defs {
         Ok(d) => d,
         Err(_) => return,
     };
 
-    let code = isle::compile::compile(&defs);
+    let code = cranelift_isle::compile::compile(&defs);
     log::debug!("code = {:?}", code);
     let code = match code {
         Ok(c) => c,