Merge pull request #2 from iris-cpp/cxx-std-flag-fix

Set CMake C++ standard flag in `PARENT_SCOPE`

Author: saki7

CMakeLists.txt

@@ -77,6 +77,10 @@ if(MSVC)
     if(CMAKE_CXX_STANDARD EQUAL ${IRIS_CXX_VERSION_BEFORE_LATEST})
         set(CMAKE_CXX${IRIS_CXX_VERSION_BEFORE_LATEST}_STANDARD_COMPILE_OPTION /std:c++${IRIS_CXX_VERSION_BEFORE_LATEST}preview)
         set(CMAKE_CXX${IRIS_CXX_VERSION_BEFORE_LATEST}_EXTENSION_COMPILE_OPTION /std:c++${IRIS_CXX_VERSION_BEFORE_LATEST}preview)
+
+        set(CMAKE_CXX${IRIS_CXX_VERSION_BEFORE_LATEST}_STANDARD_COMPILE_OPTION ${CMAKE_CXX${IRIS_CXX_VERSION_BEFORE_LATEST}_STANDARD_COMPILE_OPTION} PARENT_SCOPE)
+        set(CMAKE_CXX${IRIS_CXX_VERSION_BEFORE_LATEST}_EXTENSION_COMPILE_OPTION ${CMAKE_CXX${IRIS_CXX_VERSION_BEFORE_LATEST}_EXTENSION_COMPILE_OPTION} PARENT_SCOPE)
+
         target_compile_options(_iris_cxx_common INTERFACE /std:c++${IRIS_CXX_VERSION_BEFORE_LATEST}preview)
 
     else()