Changed compiler versions to ones that have thread_local.

dlib/use_cpp_11.cmake

@@ -27,7 +27,7 @@ include(${dlib_path}/add_global_compiler_switch.cmake)
 if (CMAKE_VERSION VERSION_LESS "3.1")
    if(CMAKE_COMPILER_IS_GNUCXX)
       execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION)
-      if (GCC_VERSION VERSION_GREATER 4.7 OR GCC_VERSION VERSION_EQUAL 4.7)
+      if (GCC_VERSION VERSION_GREATER 4.8 OR GCC_VERSION VERSION_EQUAL 4.8)
          message(STATUS "C++11 activated.")
          add_global_compiler_switch("-std=gnu++11")
          set(COMPILER_CAN_DO_CPP_11 1)
@@ -35,7 +35,7 @@ if (CMAKE_VERSION VERSION_LESS "3.1")
    elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
       execute_process( COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_VARIABLE clang_full_version_string )
       string (REGEX REPLACE ".*clang version ([0-9]+\\.[0-9]+).*" "\\1" CLANG_VERSION ${clang_full_version_string})
-      if (CLANG_VERSION VERSION_GREATER 3.1)
+      if (CLANG_VERSION VERSION_GREATER 3.3)
          message(STATUS "C++11 activated.")
          add_global_compiler_switch("-std=c++11")
          set(COMPILER_CAN_DO_CPP_11 1)