Fix -mrecip errors in clang.

Notice that currently "#" comment is parsed correctly by scram for some reason so the flags in KalmanUpdators actually are in the build.
What was the issue with the comments?
based on verbose printouts from scram, I see that 
```#<flags   CXXFLAGS="-Ofast -mrecip -funroll-all-loops"/>``` 
was actually treated as uncommented