CMakeLists.txt: set std=gnu++98

Required to fix a few errors where some enum->int->wchar_t* casting
happens.

CMakeLists.txt

@@ -56,6 +56,7 @@ set_property(TARGET ${PROJECT_NAME} mksh vroot PROPERTY INCLUDE_DIRECTORIES
   ${CMAKE_CURRENT_BINARY_DIR}
   ${BSD_INCLUDE_DIRS}
 )
+set_property(TARGET ${PROJECT_NAME} mksh vroot PROPERTY CXX_STANDARD 98)
 
 target_link_libraries(${PROJECT_NAME}
   mksh vroot pthread ${BSD_LIBRARIES} ${NSL_LIB} ${INTL_LIB}