- When HLA is enabled in Simgear, HLA is also enabled in Flightgear

making the build between Simgear and Flightgear consistent.
- Fix an issue with lib/lib64 path between CentOS/RedHat distributions
  and Debian derived distributions.

CMakeLists.txt

@@ -294,11 +294,10 @@ endif()
 if(ENABLE_RTI)
     find_package(PkgConfig)
     if(PKG_CONFIG_FOUND)
-      SET(ENV{PKG_CONFIG_PATH} "${CMAKE_INSTALL_PREFIX}/${_LIBDIR_DEFAULT}/pkgconfig:$ENV{PKG_CONFIG_PATH}")
+      SET(ENV{PKG_CONFIG_PATH} "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/pkgconfig:$ENV{PKG_CONFIG_PATH}")
       pkg_check_modules(RTI hla-rti13)
     endif(PKG_CONFIG_FOUND)
     if(RTI_FOUND)
-      SET(RTI_INCLUDE_DIR "${RTI_INCLUDE_DIRS}")
       message(STATUS "RTI: ENABLED")
     else()
       message(STATUS "RTI: DISABLED")