ci,azure-pipelines: add initial yaml file (Linux only for now)

[commodo]

Adapted from iio-osciloscope. Only building for newer Linux distros (Ubuntu 20.04 and CentOS 8), since the GnuRadio version is 3.8 in those distros and we don't want to build it (as we used to) for older distros.

Homebrew and OS X seem to require some more investigation to get the linking working.

Signed-off-by: Alexandru Ardelean alexandru.ardelean@analog.com

[commodo]

Disabled appveyor for this repo, since it's failing anyway.

For OS X builds:

• i pushed a branch here, which is this one + an OS X build : https://github.com/analogdevicesinc/gr-iio/commits/staging/azure-osx
• it looks like it needs to be run with cmake -DCMAKE_CXX_FLAGS="-std=c++11" .. ; maybe for Darwin/Apple we may encoded in the CMakLists.txt file; without -std=c++11 the error is at this link
• with "-std=c++11 it looks like there are some linker error; it can't seem to find some Gnuradio symbols; this could be related to some homebrew patch (/usr/local/lib) not being search, or I don't know; error is at this link

I guess at this point having a Mac around would be handy. For now [and for me] this year, I'll settle with 2 Linux builds for gr-iio.

[commodo]

Disabled appveyor for this repo, since it's failing anyway.

I disabled appveyor after it started. So, the failures showing up is still expected.