LTO is broken on GCC < 4.9.0, disable it.

References:

- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57038
- https://github.com/Project-OSRM/node-osrm/pull/112

CMakeLists.txt

@@ -155,6 +155,11 @@ if(CMAKE_BUILD_TYPE MATCHES Release)
       set(CMAKE_AR     "/usr/bin/gcc-ar")
       set(CMAKE_RANLIB "/usr/bin/gcc-ranlib")
     endif()
+
+    if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" AND "${CMAKE_CXX_COMPILER_VERSION}" VERSION_LESS "4.9.0")
+      message(STATUS "Disabling LTO on GCC < 4.9.0 since it is broken, see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57038")
+      set(CMAKE_CXX_FLAGS "${OLD_CXX_FLAGS}")
+    endif()
   endif()
 endif()