Use GOMA_HERMETIC=error for USE_GOMA=true build

With this flag, goma's client (gomacc) fails when local
compiler is different from goma's. Without this, goma's
backend finds a fallback compiler which looks closer to the
local compiler using version info, etc.

Bug: 25668061

Change-Id: I64ff81751f3fe960a557ddb2ca30a090c26c4327