build: replace WERROR with CMAKE_COMPILE_WARNING_AS_ERROR

-Werror is added to the previous releases job, given it runs on Ubuntu
22.04, which uses an older CMake.

`--compile-no-warning-as-error` can be used, if needed, in future, to
suppress the `CMAKE_COMPILE_WARNING_AS_ERROR` behaviour from a CI
config.

CMAKE_COMPILE_WARNING_AS_ERROR was added to CMake in 3.24.
See https://cmake.org/cmake/help/latest/prop_tgt/COMPILE_WARNING_AS_ERROR.html.

Co-authored-by: willcl-ark <will8clark@gmail.com>

ci/test/00_setup_env_native_previous_releases.sh

@@ -15,13 +15,14 @@ export TEST_RUNNER_EXTRA="--previous-releases --coverage --extended --exclude fe
 export GOAL="install"
 export CI_LIMIT_STACK_SIZE=1
 export DOWNLOAD_PREVIOUS_RELEASES="true"
+# Use -Werror as the CMake version does not support CMAKE_COMPILE_WARNING_AS_ERROR
 export BITCOIN_CONFIG="\
  --preset=dev-mode \
  -DREDUCE_EXPORTS=ON \
  -DCMAKE_BUILD_TYPE=Debug \
- -DCMAKE_C_FLAGS='-funsigned-char' \
+ -DCMAKE_C_FLAGS='-funsigned-char -Werror' \
  -DCMAKE_C_FLAGS_DEBUG='-g2 -O2' \
- -DCMAKE_CXX_FLAGS='-funsigned-char' \
+ -DCMAKE_CXX_FLAGS='-funsigned-char -Werror' \
  -DCMAKE_CXX_FLAGS_DEBUG='-g2 -O2' \
  -DAPPEND_CPPFLAGS='-DBOOST_MULTI_INDEX_ENABLE_SAFE_MODE' \
 "