Fix build of audio/clementine-player with clang 3.9.0

Clang 3.9.0 has a new warning about undefined template variables, which
is triggered by including cryptopp headers in the spotify blob
downloader:

In file included from /wrkdirs/usr/ports/audio/clementine-player/work/Clementine-1.3.1/src/internet/spotify/spotifyblobdownloader.cpp:43:
/usr/local/include/cryptopp/pkcspad.h:74:53: error: instantiation of variable 'CryptoPP::PKCS_DigestDecoration<CryptoPP::SHA512>::decoration' required here, but no definition is available [-Werror,-Wundefined-var-template]

return HashIdentifier(PKCS_DigestDecoration<H>::decoration, PKCS_DigestDecoration<H>::length);
                                                ^

This warning could be silenced by hacking on cryptopp, but just suppress
it for now.

Approved by: sbruno (maintainer)
PR: 212343
MFH: 2016Q3