FIREBREATH-221 CMake must be run twice on Linux

If CMake is only run once it creates invalid include statements.
The cause is the use of CACHE + PARENT_SCOPE on SET (they are either/or)

Fixes FIREBREATH-221

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #95 from GordonSmith/FIREBREATH-221

FIREBREATH-221 CMake must be run twice on Linux