before this change, when building the test of `view_build_test` with
clang-20, we can have following build failure:
```
FAILED: test/boost/CMakeFiles/view_build_test.dir/Debug/view_build_test.cc.o
/home/kefu/.local/bin/clang++ -DBOOST_ALL_DYN_LINK -DDEBUG -DDEBUG_LSA_SANITIZER -DFMT_SHARED -DSANITIZE -DSCYLLA_BUILD_MODE=debug -DSCYLLA_ENABLE_ERROR_INJECTION -DSEASTAR_API_LEVEL=7 -DSEASTAR_DEBUG -DSEASTAR_DEBUG_PROMISE -DSEASTAR_DEBUG_SHARED_PTR -DSEASTAR_DEFAULT_ALLOCATOR -DSEASTAR_LOGGER_COMPILE_TIME_FMT -DSEASTAR_LOGGER_TYPE_STDOUT -DSEASTAR_SCHEDULING_GROUPS_COUNT=16 -DSEASTAR_SHUFFLE_TASK_QUEUE -DSEASTAR_SSTRING -DSEASTAR_TESTING_MAIN -DSEASTAR_TYPE_ERASE_MORE -DXXH_PRIVATE_API -DCMAKE_INTDIR=\"Debug\" -I/home/kefu/dev/scylladb -I/home/kefu/dev/scylladb/build/gen -I/home/kefu/dev/scylladb/seastar/include -I/home/kefu/dev/scylladb/build/seastar/gen/include -I/home/kefu/dev/scylladb/build/seastar/gen/src -isystem /home/kefu/dev/scylladb/abseil -isystem /home/kefu/dev/scylladb/build/rust -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 -Werror=unused-result -fstack-clash-protection -fsanitize=address -fsanitize=undefined -fno-sanitize=vptr -MD -MT test/boost/CMakeFiles/view_build_test.dir/Debug/view_build_test.cc.o -MF test/boost/CMakeFiles/view_build_test.dir/Debug/view_build_test.cc.o.d -o test/boost/CMakeFiles/view_build_test.dir/Debug/view_build_test.cc.o -c /home/kefu/dev/scylladb/test/boost/view_build_test.cc
/home/kefu/dev/scylladb/test/boost/view_build_test.cc:998:5: error: unknown type name 'simple_schema'
998 | simple_schema ss;
| ^
```
apparently, `simple_schema`'s declaration is not available in this
translation unit.
in this change
* we include the header where `simple_schema` is defined, so that
the build passes with clang-20.
* also take this opportunity to reorder the header a little bit,
so the testing headers are grouped together.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#20367
e431b90145