output: log unreachable in renderExpression rather than crashing

something in std/os/windows/kernel32.zig hits an unreachable in
renderExpression. will figure it out later. for now, prefer logging an
error and continue program execution.

src/output.zig

@@ -643,19 +643,19 @@ fn renderExpression(gpa: Allocator, ais: *Ais, tree: Ast, node: Ast.Node.Index,
             return renderToken(ais, tree, main_tokens[node], space); // name
         },
 
-        .fn_decl => unreachable,
-        .container_field => unreachable,
-        .container_field_init => unreachable,
-        .container_field_align => unreachable,
-        .root => unreachable,
-        .global_var_decl => unreachable,
-        .local_var_decl => unreachable,
-        .simple_var_decl => unreachable,
-        .aligned_var_decl => unreachable,
-        .@"usingnamespace" => unreachable,
-        .test_decl => unreachable,
-        .asm_output => unreachable,
-        .asm_input => unreachable,
+        //.fn_decl => unreachable,
+        //.container_field => unreachable,
+        //.container_field_init => unreachable,
+        //.container_field_align => unreachable,
+        //.root => unreachable,
+        //.global_var_decl => unreachable,
+        //.local_var_decl => unreachable,
+        //.simple_var_decl => unreachable,
+        //.aligned_var_decl => unreachable,
+        //.@"usingnamespace" => unreachable,
+        //.test_decl => unreachable,
+        //.asm_output => unreachable,
+        //.asm_input => unreachable,
 
         else => |tag| {
             log.err("renderExpression for {} unimplemented\n", .{tag});