Perform dynamic alignment computations so that the data in TypeLocs is

correctly aligned.  Not performing such computations led to misaligned loads,
which crash on some platforms and are generally bad on other platforms.

The implementation of TypeLocBuilder::pushImpl is rather messy; code using
TypeLocBuilder accidentally assumes that partial TypeLocs are
laid out like a complete TypeLoc.  As a followup, I intend to work on
fixing the TypeLocBuilder API to avoid exposing partial TypeLocs; this should
substantially simplify the implemementation.

Fixes PR16144.

llvm-svn: 183466