when compiling date.h, clang 20 complains:
```
/home/kefu/.local/bin/clang++ -DDEBUG -DDEBUG_LSA_SANITIZER -DSANITIZE -DSCYLLA_BUILD_MODE=debug -DSCYLLA_ENABLE_ERROR_INJECTION -DXXH_PRIVATE_API -DCMAKE_INTDIR=\"Debug\" -I/home/kefu/dev/scylladb -I/home/kefu/dev/scylladb/build/gen -isystem /home/kefu/dev/scylladb/build/rust -isystem /home/kefu/dev/scylladb/seastar/include -isystem /home/kefu/dev/scylladb/build/Debug/seastar/gen/include -isystem /usr/include/p11-kit-1 -isystem /home/kefu/dev/scylladb/abseil -g -Og -g -gz -std=gnu++23 -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-unused-parameter -ffile-prefix-map=/home/kefu/dev/scylladb/build=. -march=westmere -Xclang -fexperimental-assignment-tracking=disabled -std=c++23 -Werror=unused-result -fstack-clash-protection -fsanitize=address -fsanitize=undefined -DSEASTAR_API_LEVEL=7 -DSEASTAR_BUILD_SHARED_LIBS -DSEASTAR_SSTRING -DSEASTAR_LOGGER_COMPILE_TIME_FMT -DSEASTAR_SCHEDULING_GROUPS_COUNT=16 -DSEASTAR_DEBUG -DSEASTAR_DEFAULT_ALLOCATOR -DSEASTAR_SHUFFLE_TASK_QUEUE -DSEASTAR_DEBUG_SHARED_PTR -DSEASTAR_DEBUG_PROMISE -DSEASTAR_LOGGER_TYPE_STDOUT -DSEASTAR_TYPE_ERASE_MORE -DFMT_SHARED -DWITH_GZFILEOP -MD -MT lang/CMakeFiles/lang.dir/Debug/lua.cc.o -MF lang/CMakeFiles/lang.dir/Debug/lua.cc.o.d -o lang/CMakeFiles/lang.dir/Debug/lua.cc.o -c /home/kefu/dev/scylladb/lang/lua.cc
In file included from /home/kefu/dev/scylladb/lang/lua.cc:18:
/home/kefu/dev/scylladb/utils/date.h:836:34: error: identifier '_d' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
836 | CONSTCD11 date::day operator "" _d(unsigned long long d) NOEXCEPT;
| ~~~~~~~~~~~~^~
| operator""_d
```
because, in
[CWG2521](https://wg21.link/CWG2521), it proposes that compiler should
consider
```c++
string operator "" _i18n(const char*, std::size_t); // OK, deprecated
```
as "OK, deprecated".
and Clang implemented this proposal, as it was accepted by C++23. since
scylladb uses C++23 standard. let's remove the space between `"` and
`_` to be more compliant to the C++23 standard and to silence the
warning, which is taken as an error.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#21194
5255f18c35