Make buildworld fails

Why am I getting these errors?

error: user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]

----------------------
In file included from /usr/src/usr.sbin/pmc/cmd_pmc_filter.cc:71:
In file included from
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string:477:
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string_view:796:29:
error: user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string_view<char> operator "" sv(const char *__str, size_t __len)
_NOEXCEPT
                            ^
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string_view:802:32:
error: user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string_view<wchar_t> operator "" sv(const wchar_t *__str, size_t
__len) _NOEXCEPT
                               ^
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string_view:808:33:
error: user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string_view<char16_t> operator "" sv(const char16_t *__str,
size_t __len) _NOEXCEPT
                                ^
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string_view:814:33:
error: user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string_view<char32_t> operator "" sv(const char32_t *__str,
size_t __len) _NOEXCEPT
                                ^
In file included from /usr/src/usr.sbin/pmc/cmd_pmc_filter.cc:71:
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string:4046:24: error:
user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string<char> operator "" s( const char *__str, size_t __len )
                       ^
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string:4052:27: error:
user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string<wchar_t> operator "" s( const wchar_t *__str, size_t __len
)
                          ^
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string:4058:28: error:
user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string<char16_t> operator "" s( const char16_t *__str, size_t
__len )
                           ^
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/c++/v1/string:4064:28: error:
user-defined literal suffixes not starting with '_' are reserved
[-Werror,-Wuser-defined-literals]
    basic_string<char32_t> operator "" s( const char32_t *__str, size_t
__len )
                           ^
8 errors generated.
*** Error code 1