[IR] Disallow loading and storing unsized types
Summary:
It isn't clear what is the operational meaning of loading or storing an
unsized types, since it cannot be lowered into something meaningful.
Since there does not seem to be any practical need for it either, make
such loads and stores illegal IR.
Reviewers: majnemer, chandlerc
Subscribers: mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D20846
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271402
91177308-0d34-0410-b5e6-
96231b3b80d8