several ports: clang include errors on 12

[Raif S. Berent]

Hello. I'm trying the drm-next source tree (Macy et al.)
Naturally I have to re-build all ports (appx 2100) for my testing.

Im getting a common build error for several ports (15+ so far) with fail point as "compiler include" for: xmmintrin.h emmintrin.h cpuid.h

The poudriere build environment has ccache enabled and the "missing" includes are under
~jail/usr/lib/clang/3.9.1/include/

Can anyone give some pointers where to look further? I have not tested with ccache disabled, but since some 300 ports already built without problem, I doubt the problem is ccache.
I can't tell whether the source is per port or in a MK/bsd* file, the problem involve sse2 AFIK, but world/kernel should not cause this?

Some pointers please on how to debug and I'll get to it...