stage2: tiny improvements all over the place

* pass more x64 behavior tests
* return with a TODO error when lowering a decl with no runtime bits
* insert some debug logs for tracing recursive descent down the
type-value tree when lowering types
* print `Decl`'s name when print debugging `decl_ref` value

src/codegen.zig

@@ -150,6 +150,8 @@ pub fn generateSymbol(
     const tracy = trace(@src());
     defer tracy.end();
 
+    log.debug("generateSymbol: ty = {}, val = {}", .{ typed_value.ty, typed_value.val });
+
     if (typed_value.val.isUndefDeep()) {
         const target = bin_file.options.target;
         const abi_size = try math.cast(usize, typed_value.ty.abiSize(target));
@@ -485,6 +487,18 @@ fn lowerDeclRef(
         return Result{ .appended = {} };
     }
 
+    const is_fn_body = decl.ty.zigTypeTag() == .Fn;
+    if (!is_fn_body and !decl.ty.hasRuntimeBits()) {
+        return Result{
+            .fail = try ErrorMsg.create(
+                bin_file.allocator,
+                src_loc,
+                "TODO handle void types when lowering decl ref",
+                .{},
+            ),
+        };
+    }
+
     if (decl.analysis != .complete) return error.AnalysisFail;
     decl.markAlive();
     const vaddr = vaddr: {