Based on this upstream commit:
https://github.com/MariaDB/server/commit/92d6c13206b199f24384ed2504ed479b0f59c314

--- mariadb-10.5.0/sql/CMakeLists.txt	2019-11-28 16:19:01.000000000 +0100
+++ mariadb-10.5.0/sql/CMakeLists.txt_patched	2020-01-22 00:52:28.858844312 +0100
@@ -277,7 +277,7 @@ IF(MSVC AND NOT WITHOUT_DYNAMIC_PLUGINS)
   SET_TARGET_PROPERTIES(mysqld_import_lib PROPERTIES IMPORTED_LOCATION ${MYSQLD_LIB})
 ENDIF()
 
-ADD_LIBRARY( sql_builtins  ${CMAKE_CURRENT_BINARY_DIR}/sql_builtin.cc)
+ADD_LIBRARY(sql_builtins STATIC ${CMAKE_CURRENT_BINARY_DIR}/sql_builtin.cc)
 TARGET_LINK_LIBRARIES(sql_builtins ${MYSQLD_STATIC_PLUGIN_LIBS})
 
 MYSQL_ADD_EXECUTABLE(mysqld ${MYSQLD_SOURCE} DESTINATION ${INSTALL_SBINDIR} COMPONENT Server)