updating ppport.h

[Gavin Smith]

I have attempted to follow the instructions in README-hacking to update
tp/Texinfo/XS/ppport.h:

    Update ppport.h in tp/Texinfo/XS:
      perl -MDevel::PPPort -e'Devel::PPPort::WriteFile'

However, this downgraded the version of the file.

I tried to update the version of Devel::PPPort on my system (with some
command like "sudo cpan Devel::PPPort") which was better, but it still
doesn't get to the current version, which is 3.71, while Devel::PPPort
downgrades it to 3.68.

Devel::PPPort at CPAN seems to be at 3.68:

https://metacpan.org/pod/Devel::PPPort

I don't know how to get version 3.71 or a newer version if there is one.
I will leave it at 3.68.