Apple Clang: add flags for C++17 standard

Modules/Compiler/AppleClang-CXX.cmake

@@ -25,7 +25,10 @@ elseif(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.1)
   set(CMAKE_CXX14_STANDARD__HAS_FULL_SUPPORT ON)
 endif()
 
-if (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 6.1)
+if (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 10.0)
+  set(CMAKE_CXX17_STANDARD_COMPILE_OPTION "-std=c++17")
+  set(CMAKE_CXX17_EXTENSION_COMPILE_OPTION "-std=gnu++17")
+elseif (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 6.1)
   set(CMAKE_CXX17_STANDARD_COMPILE_OPTION "-std=c++1z")
   set(CMAKE_CXX17_EXTENSION_COMPILE_OPTION "-std=gnu++1z")
 endif()

Modules/Compiler/AppleClang-OBJCXX.cmake

@@ -22,7 +22,10 @@ elseif(NOT CMAKE_OBJCXX_COMPILER_VERSION VERSION_LESS 5.1)
   set(CMAKE_OBJCXX14_STANDARD__HAS_FULL_SUPPORT ON)
 endif()
 
-if (NOT CMAKE_OBJCXX_COMPILER_VERSION VERSION_LESS 6.1)
+if (NOT CMAKE_OBJCXX_COMPILER_VERSION VERSION_LESS 10.0)
+  set(CMAKE_OBJCXX17_STANDARD_COMPILE_OPTION "-std=c++17")
+  set(CMAKE_OBJCXX17_EXTENSION_COMPILE_OPTION "-std=gnu++17")
+elseif (NOT CMAKE_OBJCXX_COMPILER_VERSION VERSION_LESS 6.1)
   set(CMAKE_OBJCXX17_STANDARD_COMPILE_OPTION "-std=c++1z")
   set(CMAKE_OBJCXX17_EXTENSION_COMPILE_OPTION "-std=gnu++1z")
 endif()