Remove .c_str() calls from log()/log_error()

There are some leftovers, but this is an easy regex-based approach that removes most of them.

docs/source/code_examples/extensions/my_cmd.cc

@@ -10,7 +10,7 @@ struct MyPass : public Pass {
     {
         log("Arguments to my_cmd:\n");
         for (auto &arg : args)
-            log("  %s\n", arg.c_str());
+            log("  %s\n", arg);
 
         log("Modules in current design:\n");
         for (auto mod : design->modules())