build: disable operator<< for vector and unordered_map

seastar provides an option named `Seastar_DEPRECATED_OSTREAM_FORMATTERS`
to enable the operator<< for `std::vector` and `std::unordered_map`,
and this option is enabled by default. but we intent to avoid using
them, so that we can use the fmt::formatter specializations when
Boost.test prints variables. if we keep these two operator<< enabled,
Boost.test would use them when printing variables to be compaired
then the check fails, but if elements in the vector or unordered_map
to be compaired does do not provide operator<<, compiling would fail.

so, in this change, let's disable these operator<< implementations.
this allows us to ditch the operator<< implementations which are
preserved only for testing.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

CMakeLists.txt

@@ -50,6 +50,7 @@ set(CMAKE_CXX_VISIBILITY_PRESET hidden)
 
 set(Seastar_TESTING ON CACHE BOOL "" FORCE)
 set(Seastar_API_LEVEL 7 CACHE STRING "" FORCE)
+set(Seastar_DEPRECATED_OSTREAM_FORMATTERS OFF CACHE BOOL "" FORCE)
 set(Seastar_APPS ON CACHE BOOL "" FORCE)
 set(Seastar_EXCLUDE_APPS_FROM_ALL ON CACHE BOOL "" FORCE)
 set(Seastar_EXCLUDE_TESTS_FROM_ALL ON CACHE BOOL "" FORCE)

configure.py

@@ -1714,6 +1714,7 @@ def configure_seastar(build_dir, mode, mode_config):
         '-DSeastar_LD_FLAGS={}'.format(semicolon_separated(mode_config['lib_ldflags'], seastar_cxx_ld_flags)),
         '-DSeastar_CXX_DIALECT=gnu++20',
         '-DSeastar_API_LEVEL=7',
+        '-DSeastar_DEPRECATED_OSTREAM_FORMATTERS=OFF',
         '-DSeastar_UNUSED_RESULT_ERROR=ON',
         '-DCMAKE_EXPORT_COMPILE_COMMANDS=ON',
         '-DSeastar_SCHEDULING_GROUPS_COUNT=16',