Use modern CMake property to handle static runtime linking with MSVC

See https://github.com/SFML/SFML/pull/1834

CMakeLists.txt

@@ -47,17 +47,6 @@ csfml_set_option(CSFML_LINK_SFML_STATICALLY ${LINK_STATICALLY_DEFAULT} BOOL "TRU
 # define an option for choosing between static and dynamic C runtime (Windows only)
 if(SFML_OS_WINDOWS)
     set(STATIC_STD_LIBS FALSE CACHE BOOL "TRUE to statically link to the standard libraries, FALSE to use them as DLLs")
-
-    # for VC++, we can apply it globally by modifying the compiler flags
-    if(SFML_COMPILER_MSVC AND STATIC_STD_LIBS)
-        foreach(flag
-                CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE
-                CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)
-            if(${flag} MATCHES "/MD")
-                string(REGEX REPLACE "/MD" "/MT" ${flag} "${${flag}}")
-            endif()
-        endforeach()
-    endif()
 endif()
 
 # find SFML libraries (C++)