Tom Finegan 2b2c196558 cmake: Fix required flag check.
It always passed after first test due to lack of CACHE in unset()
call. Also:

- Fix flag name in error message.
- Use actual flag instead of hard coded -std=c++11

Change-Id: I29c0dc4fd0f5ce97f658919a5739e15831a00281
2017-01-23 10:58:45 -08:00
..