Which gcc are you using, and how do you build the kernel ?
Reason for asking is that I don't see the problem myself.

It looks like I see them when building a v4.19 based kernel in the v3.18 repo, but not in the linux-next repo.  I'm guessing they must be using different versions of gcc.  I'll take a harder look tomorrow.

Confirmed, this happens 100% of the time when building in kernel-3_14, but not at all when building in linux-next.  Both are at the same commit id:

088c04f5bc33 CHROMIUM: Normalize defconfig

From looking at the commands being run I think they are both using the same versions of gcc and other tools.

I see the same warning whether building everything via "build_packages", or when emerging just sys-kernel/chromeos-kernel-3_14.

It turns out that this is due to the fact that sys-kernel/chromeos-kernel-3_14 creates a gcov-enabled build, while sys-kernel/chromeos-kernel-4_19 and sys-kernel/chromeos-kernel-next do not.  The latter two use clang by default, but for this testing I had them use gcc via a USE flag.

In the v3.14 repo you can avoid triggering this issue with the USE flag "-kernel_afdo".

In any case, since a) the older kernels that do use gcov don't see this, b) the more recent kernels use clang, I'll just close this as "won't fix".  We can revisit if we need to use gcov or the llvm equivalent on a recent kernel.