[OE-core] [PATCH] cmake: install path variables should be relative to the prefix path

[Clemens Lang]

Hi,

here's a patch to call CMake with relative paths for some variables.
We're using this in production since Nov 2015 without issues. We also
reported this upstream and confirmed that CMake expects relative paths.

HTH,
-- 
Clemens Lang • Development Specialist
BMW Car IT GmbH • Lise-Meitner-Str. 14 • 89081 Ulm • http://bmw-carit.com
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