security/libgpg-error: Revert use of tradcpp (F11 regression)

With the previous change, libgpg-error does not pass configure target
on FreeBSD 11 due tradcpp failing "sanity checks". This is a regression
since this port builds fine on FreeBSD 10. However, 2037 ports get
skipped (this port is *way* too important) as a result, so revert the
gcc-5 fix until a solution can be found.

PR: 197562