Revert "remove definition of LIB_NAME_shared_EXPORTS"

This reverts commit 24acdac.

Author: wgtmac

cmake_modules/BuildUtils.cmake

@@ -214,9 +214,7 @@ function(add_iceberg_lib LIB_NAME)
   # generate export header file
   if(BUILD_SHARED)
     generate_export_header(${LIB_NAME}_shared BASE_NAME ${LIB_NAME})
-    # ${LIB_NAME}_shared_EXPORTS should be defined automatically.
-    # See https://cmake.org/cmake/help/latest/prop_tgt/DEFINE_SYMBOL.html
-    # target_compile_definitions(${LIB_NAME}_shared PUBLIC ${LIB_NAME}_shared_EXPORTS)
+    target_compile_definitions(${LIB_NAME}_shared PUBLIC ${LIB_NAME}_shared_EXPORTS)
     if(BUILD_STATIC)
       string(TOUPPER ${LIB_NAME} LIB_NAME_UPPER)
       target_compile_definitions(${LIB_NAME}_static