CodeGen: Don't follow aliases when extracting type info.

This fixes a crash in the case where the type info object is an alias
pointing to a non-zero offset within a global or is otherwise unanalyzable
by the stripPointerCasts() function. Looking through the alias is not the
right thing to do anyway for similar reasons as D65118.

Differential Revision: https://reviews.llvm.org/D65314

llvm-svn: 367696