add enable_latest_cxx_support.cmake and added a comment to...

add enable_latest_cxx_support.cmake and added a comment to enable_cxx11_support.cmake to no longer use is.

cmake/enable_cxx11_support.cmake

 #######################################################################################################################
 # enable_cxx11_support.cmake
 #
+# NOTE: Do not use this routine! Use enable_latest_css_support.cmake instead, even if you only need C++11, as the
+#       compiler always uses the strictest ("oldest") specified standard if mulitple flags are given. This will create
+#       problems when combining multiple projects (libraries...) requiring different C++ standards.
+#
 # Enable C++-11 support by selecting the appropriate compiler flag. The flag will be appended to all of the following
 # cmake variables:
 # - CMAKE_CXX_FLAGS

cmake/enable_latest_cxx_support.cmake

+#######################################################################################################################
+# enable_latest_cxx_support.cmake
+#
+# Enable the latest C++ standard supported by the compiler. by selecting the appropriate compiler flag. The flag will
+# be appended to all of the following cmake variables:
+# - CMAKE_CXX_FLAGS
+# - ${PROJECT_NAME}_CXX_FLAGS
+# - ${PROJECT_NAME}_CMAKE_CXX_FLAGS
+#
+#######################################################################################################################
+
+#######################################################################################################################
+#
+# IMPORTANT NOTE:
+#
+# DO NOT MODIFY THIS FILE inside a project. Instead update the project-template repository and pull the change from
+# there. Make sure to keep the file generic, since it will be used by other projects, too.
+#
+# If you have modified this file inside a project despite this warning, make sure to cherry-pick all your changes
+# into the project-template repository immediately.
+#
+#######################################################################################################################
+
+include(CheckCXXCompilerFlag)
+CHECK_CXX_COMPILER_FLAG("-std=c++17" COMPILER_SUPPORTS_CXX17)
+CHECK_CXX_COMPILER_FLAG("-std=c++14" COMPILER_SUPPORTS_CXX14)
+CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
+CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
+if(COMPILER_SUPPORTS_CXX11)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+    set(${PROJECT_NAME}_CXX_FLAGS "${${PROJECT_NAME}_CXX_FLAGS} -std=c++11")
+    set(${PROJECT_NAME}_CMAKE_CXX_FLAGS "${${PROJECT_NAME}_CMAKE_CXX_FLAGS} -std=c++11")
+elseif(COMPILER_SUPPORTS_CXX0X)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
+    set(${PROJECT_NAME}_CXX_FLAGS "${${PROJECT_NAME}_CXX_FLAGS} -std=c++0x")
+    set(${PROJECT_NAME}_CMAKE_CXX_FLAGS "${${PROJECT_NAME}_CMAKE_CXX_FLAGS} -std=c++0x")
+else()
+    message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
+endif()