This change needs another change from pull request #81, but it's kind of
a chicken/egg scenario. The 'select's in CC_GCC_5_1 need to be
refactored a bit, and would be easier to test if gcc-5.1.0 was commited.
Most of the refactoring will happen with CC_GCC_HAS_GRAPHITE.
Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>