Speculative buildbot fix.

This wasn't failing for me with clang as the compiler. I think GCC may
disagree with clang about whether a friend declaration introduces a
declaration in the enclosing namespace (or something).

Example error:

/home/uweigand/sandbox/buildbot/clang-s390x-linux/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:950:77: error: ‘llvm::raw_ostream& llvm::slpvectorizer::operator<<(llvm::raw_ostream&, const llvm::slpvectorizer::BoUpSLP::ScheduleData&)’ should have been declared inside ‘llvm::slpvectorizer’
                                              const BoUpSLP::ScheduleData &SD) {
                                                                             ^

llvm-svn: 272767