Fix compile with CMake 3.2.1, by Kevin Seroux

Explicitly link X11, as this no longer comes with OpenGL

CMakeLists.txt

@@ -110,6 +110,7 @@ IF(APPLE)
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Linux" OR
 	${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
     find_package(Threads REQUIRED)
+    find_package(X11 REQUIRED)
     
     set(USE_DBUS_DEFAULT 1)
 

src/Main/CMakeLists.txt

@@ -130,7 +130,9 @@ endif()
 if (CRASHRPT_FOUND)
 	target_link_libraries(fgfs ${CRASHRPT_LIBRARY})
 endif()
-
+if(X11_FOUND)
+    target_link_libraries(fgfs ${X11_LIBRARIES})
+endif()
 target_link_libraries(fgfs
 	${SQLITE3_LIBRARY}
 	${SIMGEAR_LIBRARIES}

utils/fgviewer/CMakeLists.txt

@@ -42,6 +42,10 @@ else()
 endif()
 
 add_executable(fgviewer ${FGVIEWER_SOURCES} ${FGVIEWER_RTI_SOURCES})
+if(X11_FOUND)
+    target_link_libraries(fgviewer ${X11_LIBRARIES})
+endif()
+
 target_link_libraries(fgviewer
 	${SIMGEAR_LIBRARIES}
 	${OPENSCENEGRAPH_LIBRARIES}