CMake: Enable C++17 mode

CHANGELOG

@@ -6,6 +6,7 @@ innoextract 1.7 (TDB)
  - Fixed case-sensitivity in parent directory when creating subdirectories
  - Fixed .bin slice file names used with Inno Setup versions older than 4.1.7
  - Made loading of .bin slice files case-insensitive
+ - Now compiles in C++17 mode if supported
 
 innoextract 1.6 (2016-03-24)
  - Added support for Inno Setup 5.5.7 (and 5.5.8) installers

cmake/CXX11Check.cmake

@@ -26,7 +26,9 @@ set(CXX11_CHECK_DIR "${CMAKE_CURRENT_LIST_DIR}/check")
 function(enable_cxx11)
 	if(MSVC)
 		if(NOT MSVC_VERSION LESS 1600)
-			if(NOT MSVC_VERSION LESS 2000)
+			if(NOT MSVC_VERSION LESS 1911)
+				set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17")
+			elseif(NOT MSVC_VERSION LESS 1910)
 				set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++14")
 			elseif(NOT MSVC_VERSION LESS 1900)
 				# Only introduced with update 3 of MSVC 2015
@@ -35,7 +37,10 @@ function(enable_cxx11)
 			set(_HAS_CXX11 1 PARENT_SCOPE)
 		endif()
 	else()
-		add_cxxflag("-std=c++14")
+		add_cxxflag("-std=c++17")
+		if(NOT FLAG_FOUND)
+			add_cxxflag("-std=c++14")
+		endif()
 		if(NOT FLAG_FOUND)
 			add_cxxflag("-std=c++11")
 		endif()