on close inspection, it turns out that the portaudio/ directories in the
'0.53-2' branch and the 'master' branch are indeed different.
i don't know why and how they have been imported (presumably with the
'portaudio/update.sh' script, but the
portaudio/portaudio/src/common/pa_gitrevision.h now shows 'unknown'
which is not very helpful)
It looks like the script was not used nor was my update/portaudio branch merged which has the define set. The script indeed sets the PA_GIT_REVISION using the update_gitrevision.sh script in the PA repo. I had fixed several small issues with the script itself, mainly due to a file no longer being present in the new portaudio version which may have been why it wasn't used in the end.
In any case, I made a small commit directly to the 0.53-2 branch which addresses this and should be pulled into master:
dd20389559b3b293a1dd4fdc427f1881e3818bd3