Last release for gnuradio 3.7

This is the last release for gnuradio 3.7.

The next release will fit to the upcoming gnuradio 3.8

v3.7.2-rc1

This release requires at least gnuradio 3.7.x.
It makes use of the gnuradio cmake modules as far as possible to avoid updating cmake modules if gnuradio requires.

The OSX part is untested due to a lack of suitable hardware.