Bug#891728: ptlib FTBFS with glibc 2.26

[Adrian Bunk]

Source: ptlib
Version: 2.10.11~dfsg-2.1
Severity: serious
Tags: buster sid

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/ptlib.html

...
ptlib/unix/channel.cxx: In member function 'virtual PBoolean PChannel::Read(const VectorOfSlice&)':
ptlib/unix/channel.cxx:239:40: error: '::readv' has not been declared
   if (ConvertOSError(lastReadCount = ::readv(os_handle, &slices[0], slices.size()), LastReadError))
                                        ^~~~~
ptlib/unix/channel.cxx:239:40: note: suggested alternative: 'read'
   if (ConvertOSError(lastReadCount = ::readv(os_handle, &slices[0], slices.size()), LastReadError))
                                        ^~~~~
                                        read
ptlib/unix/channel.cxx: In member function 'virtual PBoolean PChannel::Write(const VectorOfSlice&)':
ptlib/unix/channel.cxx:258:22: error: '::writev' has not been declared
   while ((result = ::writev(os_handle, &slices[0], slices.size())) < 0) {
                      ^~~~~~
ptlib/unix/channel.cxx:258:22: note: suggested alternative: 'write'
   while ((result = ::writev(os_handle, &slices[0], slices.size())) < 0) {
                      ^~~~~~
                      write