Enforce being pedantic.

PiperOrigin-RevId: 740991314

Author: lszekeres

.bazelrc

@@ -18,17 +18,19 @@ common --enable_platform_specific_config
 build --action_env=CC=clang
 build --action_env=CXX=clang++
 
-# Use the C++17 standard.
+# Use the C++17 standard in a pedantic manner.
 build --cxxopt=-std=c++17
-# Warn about the extensions that are not supported in C++17.
-# TODO(b/391433873): Turn warnings into errors once existing warnings are fixed.
-build --cxxopt=-Wc++17-compat-pedantic
+build --cxxopt=-Wpedantic
+build --cxxopt=-Werror=pedantic
+build --cxxopt=-Wno-error=gcc-compat
 # Required by the cc_fuzztest_grammar_library rule, which uses the
 # "exec configuration" (https://bazel.build/reference/be/general#cross-compilation-considerations).
 # The --cxxopt flag does not apply to the exec configuration, only the
 # --host_cxxopt flag (https://bazel.build/docs/user-manual#host-cxxopt).
 build --host_cxxopt=-std=c++17
-build --host_cxxopt=-Wc++17-compat-pedantic
+build --host_cxxopt=-Wpedantic
+build --host_cxxopt=-Werror=pedantic
+build --host_cxxopt=-Wno-error=gcc-compat
 
 # Build GoogleTest with ABSL support.
 build --define absl=1