mainsysutils/freefilesync: unbreak build on 10.x

error: invalid value 'c++14' in '-std=c++14'

../../zen/file_access.cpp:893:15: error: no member named 'futimens' in the global namespace

if (::futimens(fdFile, newTimes) != 0)
    ~~^

../../zen/file_access.cpp:898:15: error: no member named 'utimensat' in the global namespace

if (::utimensat(AT_FDCWD, filePath.c_str(), newTimes, AT_SYMLINK_NOFOLLOW) != 0)
    ~~^

2 errors generated.

PR: 207879
Reported by: pkg-fallout
Approved by: kevlo (maintainer, previous version)