Use the same ABI for static and shared libraries on non-Windows platforms.

src/google/protobuf/arena.cc

@@ -519,7 +519,7 @@ ThreadSafeArena::ThreadCache& ThreadSafeArena::thread_cache() {
       new internal::ThreadLocalStorage<ThreadCache>();
   return *thread_cache_->Get();
 }
-#elif defined(PROTOBUF_USE_DLLS)
+#elif defined(PROTOBUF_USE_DLLS) && defined(_MSC_VER)
 ThreadSafeArena::ThreadCache& ThreadSafeArena::thread_cache() {
   static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache;
   return thread_cache;

src/google/protobuf/reflection_mode.cc

@@ -39,7 +39,7 @@ namespace internal {
 
 #if !defined(PROTOBUF_NO_THREADLOCAL)
 
-#if defined(PROTOBUF_USE_DLLS)
+#if defined(PROTOBUF_USE_DLLS) && defined(_MSC_VER)
 ReflectionMode& ScopedReflectionMode::reflection_mode() {
   static PROTOBUF_THREAD_LOCAL ReflectionMode reflection_mode =
       ReflectionMode::kDefault;

src/google/protobuf/reflection_mode.h

@@ -95,18 +95,20 @@ class PROTOBUF_EXPORT ScopedReflectionMode final {
  private:
 #if !defined(PROTOBUF_NO_THREADLOCAL)
   const ReflectionMode previous_mode_;
-#if defined(PROTOBUF_USE_DLLS)
+#if defined(PROTOBUF_USE_DLLS) && defined(_MSC_VER)
+  // Thread local variables cannot be exposed through MSVC DLL interface but we
+  // can wrap them in static functions.
   static ReflectionMode& reflection_mode();
 #else
   PROTOBUF_CONSTINIT static PROTOBUF_THREAD_LOCAL ReflectionMode
       reflection_mode_;
-#endif  // PROTOBUF_USE_DLLS
+#endif  // PROTOBUF_USE_DLLS && _MSC_VER
 #endif  // !PROTOBUF_NO_THREADLOCAL
 };
 
 #if !defined(PROTOBUF_NO_THREADLOCAL)
 
-#if defined(PROTOBUF_USE_DLLS)
+#if defined(PROTOBUF_USE_DLLS) && defined(_MSC_VER)
 
 inline ScopedReflectionMode::ScopedReflectionMode(ReflectionMode mode)
     : previous_mode_(reflection_mode()) {
@@ -140,7 +142,7 @@ inline ReflectionMode ScopedReflectionMode::current_reflection_mode() {
   return reflection_mode_;
 }
 
-#endif  // PROTOBUF_USE_DLLS
+#endif  // PROTOBUF_USE_DLLS && _MSC_VER
 
 #else
 

src/google/protobuf/thread_safe_arena.h

@@ -261,9 +261,9 @@ class PROTOBUF_EXPORT ThreadSafeArena {
   // iOS does not support __thread keyword so we use a custom thread local
   // storage class we implemented.
   static ThreadCache& thread_cache();
-#elif defined(PROTOBUF_USE_DLLS)
-  // Thread local variables cannot be exposed through DLL interface but we can
-  // wrap them in static functions.
+#elif defined(PROTOBUF_USE_DLLS) && defined(_MSC_VER)
+  // Thread local variables cannot be exposed through MSVC DLL interface but we
+  // can wrap them in static functions.
   static ThreadCache& thread_cache();
 #else
   PROTOBUF_CONSTINIT static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache_;