PR merged: https://github.com/groonga/groonga/pull/2790.patch
The ODR violation happens because function pointer types like `grn_tokenizer_init_func` take `grn_tokenizer_query` as an argument,
and `grn_tokenizer_query` has two different definitions.
Include `grn_tokenizer.h` from `grn_db.h` so that the non-deprecated definition is always used.
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -562,6 +562,18 @@ if(GRN_WITH_UBSAN)
   endif()
 endif()
 
+option(GRN_WITH_LTO "Enable link-time optimization" OFF)
+if(GRN_WITH_LTO)
+  include(CheckIPOSupported)
+  check_ipo_supported(RESULT lto_supported OUTPUT lto_error)
+  if(lto_supported)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ON)
+  else()
+    message(FATAL_ERROR "LTO not supported: ${lto_error}")
+  endif()
+  check_build_flag("-Werror=odr")
+endif()
+
 if(WIN32)
   target_link_libraries(grn_dependencies INTERFACE dbghelp.lib)
   target_link_libraries(grn_dependencies INTERFACE psapi.lib)
--- a/lib/grn_db.h
+++ b/lib/grn_db.h
@@ -21,6 +21,8 @@
 
 #include "grn.h"
 
+#include "grn_tokenizer.h"
+
 #include "grn_ctx.h"
 #include "grn_options.h"
 #include "grn_rset.h"