$NetBSD$

Remove obsolete variable.

--- tools/CMakeLists.txt.orig	2025-08-06 11:04:19.454854216 +0000
+++ tools/CMakeLists.txt
@@ -5,7 +5,7 @@ if(MINIMAL_BUILD)
 else(MINIMAL_BUILD)
   find_package(Boost COMPONENTS program_options iostreams)
   if(Boost_FOUND)
-    include_directories(${Boost_INCLUDE_DIRS} ${Boost_INCLUDE_DIR})
+    include_directories(${Boost_INCLUDE_DIRS})
   endif()