x86intrin.h not found after 10.4->11.2 upgrade

[Morgan Reed]

Hi All,

      Finally got around to upgrading my NAS which was running FreeBSD 10.4
to a supported version (11.2).

Ran into an issue when I came to do a portupgrade -a to update all my
installed ports, a number of the ports are failing with "x86intrin.h No
such file or directory", not sure what's going on there.

I've updated my src tree just in case it was something that only got added
in 11, no change.

All the similar reports I found online were related to OLD versions of gcc
(e.g. 4.3), which is not relevant since we're using clang (I assume
anyway), but I reinstalled llvm60 from package just in case, no change
again.

An pointers would be greatly appreciated, thanks.

Morgan