Struct-path aware TBAA: uniformize scalar tag and path tag.

For struct-path aware TBAA, we used to use scalar type node as the scalar tag,
which has an incompatible format with the struct path tag. We now use the same
format: base type, access type and offset.

We also uniformize the scalar type node and the struct type node: name, a list
of pairs (offset + pointer to MDNode). For scalar type, we have a single pair.
These are to make implementaiton of aliasing rules easier.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179335 91177308-0d34-0410-b5e6-96231b3b80d8
Flail at trying to appease various linuxy buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179338 91177308-0d34-0410-b5e6-96231b3b80d8
Test case for r179339.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179340 91177308-0d34-0410-b5e6-96231b3b80d8
Add test case for r179343.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179344 91177308-0d34-0410-b5e6-96231b3b80d8