Fix build with Boost 1.91
Add X11BASE include directory

Index: GG/CMakeLists.txt
--- GG/CMakeLists.txt.orig
+++ GG/CMakeLists.txt
@@ -66,7 +66,7 @@ endif()
 
 set(MINIMUM_BOOST_VERSION 1.69.0)
 
-find_package(Boost ${MINIMUM_BOOST_VERSION} COMPONENTS filesystem regex system REQUIRED)
+find_package(Boost ${MINIMUM_BOOST_VERSION} COMPONENTS filesystem regex REQUIRED)
 
 find_package(OpenGL REQUIRED)
 find_package(GLEW REQUIRED)
@@ -89,6 +89,7 @@ endif()
 include_directories(
     ${CMAKE_CURRENT_SOURCE_DIR}
     ${CMAKE_CURRENT_BINARY_DIR}
+    ${X11BASE}/include
 )
 
 configure_file(
