CMake: Modernize C++17 standard enforcement; require VS 2019

Replaces manual compiler flag detection with target_compile_features(cxx_std_17) and sets CXX_EXTENSIONS OFF for standards compliance. Updates minimum MSVC requirement to 1920 (Visual Studio 2019).

Addresses #2211

Author: andrewfb

proj/cmake/libcinder_target.cmake

@@ -72,57 +72,15 @@ elseif( CINDER_COCOA_TOUCH )
 elseif( CINDER_LINUX )
 endif()
 
-# Check compiler support for enabling c++11 or c++14 or c++17.
+# Enforce the minimum C++ standard Cinder requires.
 if( CINDER_MSW AND MSVC )
-    if( MSVC_VERSION LESS 1800 ) # Older version of Visual Studio
-        message( FATAL_ERROR "Unsupported MSVC version: ${MSVC_VERSION}" )
-    elseif( MSVC_VERSION LESS 1900 ) # Visual Studio 2013
-        set( COMPILER_SUPPORTS_CXX11 true )
-    elseif( MSVC_VERSION LESS 1920 ) # Visual Studio 2015
-        set( COMPILER_SUPPORTS_CXX14 true )
-        set( COMPILER_SUPPORTS_CXX11 true )
-    else() # Visual Studio 2019
-        set( COMPILER_SUPPORTS_CXX17 true )
-        set( COMPILER_SUPPORTS_CXX14 true )
-        set( COMPILER_SUPPORTS_CXX11 true )
+    if( MSVC_VERSION LESS 1920 )
+        message( FATAL_ERROR "Cinder requires Visual Studio 2019 (MSVC 19.20) or newer." )
     endif()
-elseif( CINDER_ANDROID )
-	# Assume true for Android since compiler is Clang 3.8 at minimum
-   	set( COMPILER_SUPPORTS_CXX14 true )
-    set( COMPILER_SUPPORTS_CXX11 true )
-else()
-    include( CheckCXXCompilerFlag )
-    CHECK_CXX_COMPILER_FLAG( "-std=c++17" COMPILER_SUPPORTS_CXX17 )
-    CHECK_CXX_COMPILER_FLAG( "-std=c++14" COMPILER_SUPPORTS_CXX14 )
-    CHECK_CXX_COMPILER_FLAG( "-std=c++11" COMPILER_SUPPORTS_CXX11 )
 endif()
 
-if( COMPILER_SUPPORTS_CXX17 )
-    if( NOT MSVC )
-        set( CINDER_CXX_FLAGS "-std=c++17" )
-    else()
-        set( CINDER_CXX_FLAGS "/std:c++17" )
-    endif()
-elseif( COMPILER_SUPPORTS_CXX14 )
-    if( NOT MSVC )
-        set( CINDER_CXX_FLAGS "-std=c++14" )
-    else()
-        set( CINDER_CXX_FLAGS "/std:c++14")
-    endif()
-elseif( COMPILER_SUPPORTS_CXX11 )
-    if( NOT MSVC )
-        set( CINDER_CXX_FLAGS "-std=c++11" )
-    else()
-        set( CINDER_CXX_FLAGS "/std:c++11")
-    endif()
-else()
-	message( FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has neither C++11 or C++14 or C++17 support. Please use a different C++ compiler." )
-endif()
-
-# TODO: it would be nice to the following, but we can't until min required cmake is 3.3
-#target_compile_options( cinder PUBLIC $<$<COMPILE_LANGUAGE:CXX>:${CINDER_CXX_FLAGS}> )
-set( CMAKE_CXX_FLAGS "${CINDER_CXX_FLAGS} ${CMAKE_CXX_FLAGS}" )
-target_compile_options( cinder INTERFACE ${CINDER_CXX_FLAGS} )
+target_compile_features( cinder PUBLIC cxx_std_17 )
+set_property( TARGET cinder PROPERTY CXX_EXTENSIONS OFF )
 
 # This file will contain all dependencies, includes, definition, compiler flags and so on..
 export( TARGETS cinder FILE ${PROJECT_BINARY_DIR}/${CINDER_LIB_DIRECTORY}/cinderTargets.cmake )