Upstream libc++ added a using ::timespec_get line, when in C++17 or
higher mode, in https://reviews.llvm.org/rL338419. Since we do not
yet have this C11 function, comment out the line for now, as a
workaround for a number of failing ports. Discussion with upstream is
ongoing about an acceptable permanent fix.

PR: 230400
Reported by: jbeich