[Bug]: Missing Symbol When Building with MinGW on Windows

[CrSjimo]

Describe the issue

When building the monolithic shared library with MinGW, an error occurs:

ld.exe: absl/CMakeFiles/abseil_dll.dir/time/internal/cctz/src/time_zone_lookup.cc.obj: in function `absl::lts_20260107::time_internal::cctz::local_time_zone()':
absl/time/internal/cctz/src/time_zone_lookup.cc:168:(.text+0x29d): undefined reference to `absl::lts_20260107::time_internal::cctz::GetWindowsLocalTimeZone[abi:cxx11]()'

And I check the build directory, finding that time_zone_name_win.cc.obj, which contains this symbol and should be compiled, is not compiled.

Steps to reproduce the problem

1. Use CMake to configure the project with -DABSL_BUILD_MONOLITHIC_SHARED_LIBS:BOOL=ON -DBUILD_SHARED_LIBS:BOOL=ON
2. Build all

What version of Abseil are you using?

20260107.1

What operating system and version are you using?

Windows 11

What compiler and version are you using?

MinGW 15.2.0

What build system are you using?

CMake 4.1.1

Additional context

No response

[kdombroski]

Edit cmake/AbseilDll.cmake, line 468

Replace
if(MSVC)
with
if(MSVC OR MINGW)

Maybe the condition should be if(Windows) ?
I'm not sure which is best.

[kdombroski]

Proposed solution:

--- a/CMake/AbseilDll.cmake     2026-03-19 21:49:10.935877812 +1300
+++ b/CMake/AbseilDll.cmake     2026-03-19 21:49:00.919058074 +1300
@@ -457,12 +457,14 @@ set(ABSL_INTERNAL_DLL_FILES
   "strings/string_view.h"
 )
 
-if(MSVC)
+if(Windows)
   list(APPEND ABSL_INTERNAL_DLL_FILES
     "time/internal/cctz/src/time_zone_name_win.cc"
     "time/internal/cctz/src/time_zone_name_win.h"
   )
-else()
+endif()
+
+if(NOT MSVC)
   list(APPEND ABSL_INTERNAL_DLL_FILES
     "flags/commandlineflag.cc"
     "flags/commandlineflag.h"