"g++-6"  -ftemplate-depth-512 -fvisibility-inlines-hidden -std=c++14 -fPIC -m64 -pthread -O0 -fno-inline -Wall -fvisibility=hidden -Wno-maybe-uninitialized -DBOOST_ALL_NO_LIB=1 -DBOOST_CHRONO_DYN_LINK=1 -DBOOST_CHRONO_NO_LIB=1 -DBOOST_COBALT_USE_STD_PMR=1 -DBOOST_REGEX_NO_LIB=1 -DBOOST_SYSTEM_DYN_LINK=1 -DBOOST_SYSTEM_NO_LIB=1 -DBOOST_THREAD_BUILD_DLL=1 -DBOOST_THREAD_POSIX -DBOOST_THREAD_USE_DLL=1   -I".." -I"../libs/spirit/test/x3" -I"/var/boost/run/boost_root/libs/assert/include" -I"/var/boost/run/boost_root/libs/bind/include" -I"/var/boost/run/boost_root/libs/chrono/include" -I"/var/boost/run/boost_root/libs/container_hash/include" -I"/var/boost/run/boost_root/libs/core/include" -I"/var/boost/run/boost_root/libs/describe/include" -I"/var/boost/run/boost_root/libs/detail/include" -I"/var/boost/run/boost_root/libs/endian/include" -I"/var/boost/run/boost_root/libs/function/include" -I"/var/boost/run/boost_root/libs/function_types/include" -I"/var/boost/run/boost_root/libs/fusion/include" -I"/var/boost/run/boost_root/libs/integer/include" -I"/var/boost/run/boost_root/libs/iterator/include" -I"/var/boost/run/boost_root/libs/move/include" -I"/var/boost/run/boost_root/libs/mp11/include" -I"/var/boost/run/boost_root/libs/optional/include" -I"/var/boost/run/boost_root/libs/phoenix/include" -I"/var/boost/run/boost_root/libs/predef/include" -I"/var/boost/run/boost_root/libs/ratio/include" -I"/var/boost/run/boost_root/libs/regex/include" -I"/var/boost/run/boost_root/libs/smart_ptr/include" -I"/var/boost/run/boost_root/libs/spirit/include" -I"/var/boost/run/boost_root/libs/system/include" -I"/var/boost/run/boost_root/libs/throw_exception/include" -I"/var/boost/run/boost_root/libs/tuple/include" -I"/var/boost/run/boost_root/libs/type_index/include" -I"/var/boost/run/boost_root/libs/type_traits/include" -I"/var/boost/run/boost_root/libs/unordered/include" -I"/var/boost/run/boost_root/libs/variant/include" -I"/var/boost/run/boost_root/libs/variant2/include" -I"/var/boost/run/boost_root/libs/winapi/include"  -c -o "/var/boost/run/results/boost/bin.v2/libs/spirit/test/x3/x3_seek.test/gcc-6~c++14/debug/x86_64/debug-symbols-off/threading-multi/visibility-hidden/seek.o" "../libs/spirit/test/x3/seek.cpp"

In file included from ../boost/spirit/home/x3/core/skip_over.hpp:12:0,
                 from ../boost/spirit/home/x3/auxiliary/eoi.hpp:11,
                 from ../libs/spirit/test/x3/seek.cpp:10:
../boost/spirit/home/x3/support/expectation.hpp:40:20: fatal error: optional: No such file or directory
 #include <optional>
                    ^
compilation terminated.