orb_slam3：error: ‘decay_t’ is not a member of ‘std

出现bug:
这里参考了https://blog.youkuaiyun.com/qq_15987811/article/details/122937722

修改C++版本：

CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX11)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
   add_definitions(-DCOMPILEDWITHC11)
   message(STATUS "Using flag -std=c++11.")
elseif(COMPILER_SUPPORTS_CXX0X)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
   add_definitions(-DCOMPILEDWITHC0X)
   message(STATUS "Using flag -std=c++0x.")

修改成：
CHECK_CXX_COMPILER_FLAG("-std=c++14" COMPILER_SUPPORTS_CXX14)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
#CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX14)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
   add_definitions(-DCOMPILEDWITHC11)
   message(STATUS "Using flag -std=c++14.")
#elseif(COMPILER_SUPPORTS_CXX0X)
  #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
  #add_definitions(-DCOMPILEDWITHC0X)
   # message(STATUS "Using flag -std=c++0x.")

编译成功：