am 21b97ed5: Add __attribute__((format(printf, a, b))) to printf like functions.

Merge commit '21b97ed5693d039e8b9dea57a160d3307f412682'

* commit '21b97ed5693d039e8b9dea57a160d3307f412682':
  Add __attribute__((format(printf, a, b))) to printf like functions.