ci: make fuzzing builds stricter by enabling -Werror by default

Unfortunately, we need -Wno-unused-command-line-argument as configure will fail to run
with -Werror due to Dash's current build system utilizing -static-libstdc++ indiscriminately,
resulting in Clang warnings of "unused arguments".

Author: kwvg

ci/test/00_setup_env_native_fuzz.sh

@@ -9,6 +9,7 @@ export LC_ALL=C.UTF-8
 export PACKAGES="clang llvm python3 libevent-dev bsdmainutils libboost-filesystem-dev libboost-test-dev libboost-thread-dev"
 export DEP_OPTS="NO_UPNP=1 DEBUG=1"
 export CPPFLAGS="-DDEBUG_LOCKORDER -DENABLE_DASH_DEBUG -DARENA_DEBUG"
+export CXXFLAGS="-Werror -Wno-unused-command-line-argument"
 export PYZMQ=true
 export RUN_UNIT_TESTS=false
 export RUN_INTEGRATION_TESTS=false