when compiling the tree with clang-18 and ragel 6.10, the compiler
warns like:
```
/usr/local/bin/cmake -E __run_co_compile --tidy="clang-tidy-18;--checks=-*,bugprone-use-after-move;--extra-arg-before=--driver-mode=g++" --source=/home/runner/work/scylladb/scylladb/redis/controller.cc -- /usr/bin/clang++-18 -DBOOST_NO_CXX98_FUNCTION_BASE -DSCYLLA_BUILD_MODE=release -DSEASTAR_API_LEVEL=7 -DSEASTAR_LOGGER_COMPILE_TIME_FMT -DSEASTAR_LOGGER_TYPE_STDOUT -DSEASTAR_SCHEDULING_GROUPS_COUNT=16 -DSEASTAR_SSTRING -DXXH_PRIVATE_API -I/home/runner/work/scylladb/scylladb -I/home/runner/work/scylladb/scylladb/build/gen -I/home/runner/work/scylladb/scylladb/seastar/include -I/home/runner/work/scylladb/scylladb/build/seastar/gen/include -I/home/runner/work/scylladb/scylladb/build/seastar/gen/src -isystem /home/runner/work/scylladb/scylladb/cooking/include -ffunction-sections -fdata-sections -O3 -g -gz -std=gnu++20 -fvisibility=hidden -Wall -Werror -Wextra -Wno-error=deprecated-declarations -Wimplicit-fallthrough -Wno-c++11-narrowing -Wno-deprecated-copy -Wno-mismatched-tags -Wno-missing-field-initializers -Wno-overloaded-virtual -Wno-unsupported-friend -Wno-enum-constexpr-conversion -Wno-unused-parameter -ffile-prefix-map=/home/runner/work/scylladb/scylladb=. -march=westmere -mllvm -inline-threshold=2500 -fno-slp-vectorize -U_FORTIFY_SOURCE -Werror=unused-result -MD -MT redis/CMakeFiles/redis.dir/controller.cc.o -MF redis/CMakeFiles/redis.dir/controller.cc.o.d -o redis/CMakeFiles/redis.dir/controller.cc.o -c /home/runner/work/scylladb/scylladb/redis/controller.cc
error: too many errors emitted, stopping now [clang-diagnostic-error]
Error: /home/runner/work/scylladb/scylladb/build/gen/redis/protocol_parser.hh:110:1: error: unannotated fall-through between switch labels [clang-diagnostic-implicit-fallthrough]
110 | case 1:
| ^
/home/runner/work/scylladb/scylladb/build/gen/redis/protocol_parser.hh:110:1: note: insert 'FMT_FALLTHROUGH;' to silence this warning
110 | case 1:
| ^
| FMT_FALLTHROUGH;
```
since we have `-Werror`, the warnings like this are considered as error,
hence the build fails. in order to address this failure, let's silence
this warning when including this generated header file.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18447
af5674211d