DIBuilder: Similar to createPointerType, make createMemberPointerType take
a size and alignment. Several assertions in DwarfDebug rely on all variable
types to report back a size, or to be derived from a type with a size.

Tested in CFE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224780 91177308-0d34-0410-b5e6-96231b3b80d8