Internal C++ warnings cleanup

PiperOrigin-RevId: 889816903

Author: FuzzTest Team

grammar_codegen/generated_antlr_parser/BUILD

@@ -39,7 +39,6 @@ cc_library(
         # FIXME: antlr generates broken C++ code that attempts to construct
         # a std::string from nullptr. It's not clear whether the relevant
         # constructs are reachable.
-        "-Wno-nonnull",
     ],
     features = ["-use_header_modules"],  # Incompatible with -fexceptions.
     deps = ["@antlr_cpp//:antlr4-cpp-runtime"],