C++11: turn off error warning for only the error we want to turn off

previously was setting -Wno-error to get arround C++11 narrowing violations

Change-Id: I620b1d524bce4642f3f0b4af446e00394177e42b
clang: Silent warnings

Change-Id: Ic132d9bc983f1c1d9ba5d84e5f8425dc3ba002c4