Updating dpkg-buildflags to enable reproducible=+fixfilepath by default

[Lisandro Damián Nicanor Pérez Meyer]

Oh, I have sadly forgotten to mention another thing.

On Sat, 9 Jan 2021 at 15:53, Lisandro Damián Nicanor Pérez Meyer
<perezmeyer at gmail.com> wrote:
> # __FILE__ is a public, well defined API

According to:
Adrian Bunks mentions it in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876901#10
Holger Levsen in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876901#42
Mattia Rizzolo on https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876901#192

The ability of gcc to change __FILE__ was a patch that, at the time of
those writings, wasn't yet accepted.

Even more, Ximion Luo wrote on
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876901#212

  The GCC patch (neither the previous nor the planned version) does
not change the
  default behaviour of __FILE__, and was never intended to. Instead,
it gives users
  the ability to rewrite __FILE__, more specifically a prefix of it.

makes it clear that the default behaviour is not changed. So if the
patch got accepted
(did it get accepted?) it was only to allow reproducible people to
break API in order to
get reproducibility. This in itself, if something has not changed in
the meantime, marks
another reference that __FILE__ is a public, well defined API.