CMake: explicitly link Boost libraries

Explicitly link Boost libraries for programs that need it to prevent
"undefined reference to `boost::system::get_system_category()'" error
messages from appearing.

src/Airports/GenAirports850/CMakeLists.txt

@@ -32,6 +32,7 @@ target_link_libraries(genapts850
     ${CMAKE_THREAD_LIBS_INIT}
     ${SIMGEAR_CORE_LIBRARIES}
     ${SIMGEAR_CORE_LIBRARY_DEPENDENCIES}
+    ${Boost_LIBRARIES}
     ${RT_LIBRARY})
 
 install(TARGETS genapts850 RUNTIME DESTINATION bin)

src/Prep/OGRDecode/CMakeLists.txt

@@ -8,6 +8,7 @@ target_link_libraries(ogr-decode
     ${CMAKE_THREAD_LIBS_INIT}
     ${SIMGEAR_CORE_LIBRARIES}
     ${SIMGEAR_CORE_LIBRARY_DEPENDENCIES}
+    ${Boost_LIBRARIES}
 )
 
 install(TARGETS ogr-decode RUNTIME DESTINATION bin)