Remove OnDiskHashTable.h, since it's been moved to llvm

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206637 91177308-0d34-0410-b5e6-96231b3b80d8
Teach users of OnDiskHashTable to define hash_value and offset types

This paves the way to making OnDiskHashTable work with hashes that are
not 32 bits wide and to making OnDiskHashTable work very large hash
tables. The LLVM change to use these types is upcoming.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206640 91177308-0d34-0410-b5e6-96231b3b80d8
Don't read CompilerInstance fields that don't exist in ASTUnit

When transferring data from a CompilerInstance in an error path we need
to consider cases where the various fields are uninitialized.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206644 91177308-0d34-0410-b5e6-96231b3b80d8