Updating armadillo version and force source.

The armadillo .deb package does not suffice for gnss-sdr.
Also updating to a newer, maintained version.
Adding DISABLE_OPENCL option.

gnss-sdr will not compile on Debian without this option set.
See also:
https://sourceforge.net/p/gnss-sdr/mailman/message/31989872/
https://sourceforge.net/p/gnss-sdr/mailman/message/32107975/
Merge pull request #86 from lakoon/patch-2

Fixing gnss-sdr compilation errors.