error: unknown warning group '-Wcpp', ignored (#pragma GCC)

With CLANG on FreeBSD 10.0-CURRENT r250968, I get this error message in
a source I try to port.

I did not find any suitable "official" workaround and I'd like to avoid
patching all files containing those #pragma statements. Is there a
geenral solution on FreeBSD to overcome this?

error: unknown warning group '-Wcpp', ignored
[-Werror,-Wunknown-pragmas]
#  pragma GCC diagnostic ignored "-Wcpp"


Thanks in advance,
Oliver