Resubmit "[pdb] Allow zero-copy read support for symbol streams.""

Resubmit "[pdb] Allow zero-copy read support for symbol streams.""

Due to differences in template instantiation rules, it is not
portable to static_assert(false) inside of an invalid specialization
of a template.  Instead I just =delete the method so that it can't
be used, and leave a comment that it must be explicitly specialized.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271027 91177308-0d34-0410-b5e6-96231b3b80d8