[Support] Move DJB hash to support. NFC

This patch moves the DJB hash to support. This is consistent with other
hashing algorithms living there. The hash is used by the DWARF
accelerator tables. We're doing this now because the hashing function is
needed by dsymutil and we don't want to link against libBinaryFormat.

Differential revision: https://reviews.llvm.org/D42594

llvm-svn: 323616