ports: clang: error: unsupported option '-dumpspecs'

Since a couple of days now I see this happen on FreeBSD
10.0-CURRENT/amd64 (CLANG) (most recent buildworld and potstree) and
also on FreeBSD 9.0-RC[2|3]/amd64 (also CLANG built, most recent portstree):

Building new INDEX files... DESCRIBE.7 INDEX-8 not provided by portsnap
server; INDEX-7 not being generated.
done.
===>>> Gathering distinfo list for installed ports

===>>> Starting check of installed ports for available updates
clang: error: unsupported option '-dumpspecs'
clang: error: no input files

===>>> All ports are up to date


Regards,
Oliver