Include flags in DLL build (non-Windows only)

On Windows flags will likely never be compatible due to the typeid issues.

PiperOrigin-RevId: 638326696
Change-Id: If605d612af2efa4d60483ca4a03daf58511eda51

CMake/AbseilDll.cmake

@@ -440,6 +440,43 @@ set(ABSL_INTERNAL_DLL_FILES
   "debugging/leak_check.cc"
 )
 
+if(NOT MSVC)
+  list(APPEND ABSL_INTERNAL_DLL_FILES
+    "flags/commandlineflag.cc"
+    "flags/commandlineflag.h"
+    "flags/config.h"
+    "flags/declare.h"
+    "flags/flag.h"
+    "flags/internal/commandlineflag.cc"
+    "flags/internal/commandlineflag.h"
+    "flags/internal/flag.cc"
+    "flags/internal/flag.h"
+    "flags/internal/parse.h"
+    "flags/internal/path_util.h"
+    "flags/internal/private_handle_accessor.cc"
+    "flags/internal/private_handle_accessor.h"
+    "flags/internal/program_name.cc"
+    "flags/internal/program_name.h"
+    "flags/internal/registry.h"
+    "flags/internal/sequence_lock.h"
+    "flags/internal/usage.cc"
+    "flags/internal/usage.h"
+    "flags/marshalling.cc"
+    "flags/marshalling.h"
+    "flags/parse.cc"
+    "flags/parse.h"
+    "flags/reflection.cc"
+    "flags/reflection.h"
+    "flags/usage.cc"
+    "flags/usage.h"
+    "flags/usage_config.cc"
+    "flags/usage_config.h"
+    "log/flags.cc"
+    "log/flags.h"
+    "log/internal/flags.h"
+  )
+endif()
+
 set(ABSL_INTERNAL_DLL_TARGETS
   "absl_check"
   "absl_log"
@@ -602,6 +639,26 @@ set(ABSL_INTERNAL_DLL_TARGETS
   "vlog_config_internal"
 )
 
+if(NOT MSVC)
+  list(APPEND ABSL_INTERNAL_DLL_TARGETS
+    "flags"
+    "flags_commandlineflag"
+    "flags_commandlineflag_internal"
+    "flags_config"
+    "flags_internal"
+    "flags_marshalling"
+    "flags_parse"
+    "flags_path_util"
+    "flags_private_handle_accessor"
+    "flags_program_name"
+    "flags_reflection"
+    "flags_usage"
+    "flags_usage_internal"
+    "log_internal_flags"
+    "log_flags"
+  )
+endif()
+
 set(ABSL_INTERNAL_TEST_DLL_FILES
   "hash/hash_testing.h"
   "log/scoped_mock_log.cc"