Cannot buildworld 11-STABLE on 11.0-RELEASE

I was trying to perform a (source based) upgrade from 11.0-RELEASE-p8 to 11-STABLE.
I checked out svn:// in /usr/src, then trying to buildworld I got this

# svn up /usr/src
Updating '.':
At revision 316019.
# make -j3 buildworld
--- ---
Included from /usr/src/contrib/llvm/lib/Target/AArch64/
Included from /usr/src/contrib/llvm/include/llvm/Target/
Included from /usr/src/contrib/llvm/include/llvm/IR/
/usr/src/contrib/llvm/include/llvm/IR/ error: Record `int_aarch64_clrex' does not have a field named `Properties'!
def int_aarch64_clrex : Intrinsic<[]>;
*** [] Error code 1

I understand that is something related to llvm and arm64 (this machine is amd64, though), but I have no idea how to fix this problem. The compiler I'm using is the stock clang 38 found on FreeBSD 11.0-RELEASE
Did you make sure you had a clean environment ( make clean) before starting the build?

Is there anything in /etc/make.conf and/or /etc/src.conf?
I thought that clean were a buildworld's dependency! I destroyed the zfs dataset for /usr/obj and I started all over from scratch. Now it's going well, thank you.