Tools: bring OSX back to 5.3.1

There is a regression in Qt 5.3.2 for OSX that triggers
segfaults from the serial port when polling the available
ports.

https://codereview.qt-project.org/#/c/95729/

However, 5.3.2 resolved some UI bugs on Linux. Thus, it makes
sense to run separate versions for the time being. Hopefully
this can be dropped with 5.3.3