Debug info: fix a crasher when when emitting debug info for
not-yet-completed templated types. getTypeSize() needs a complete type.

rdar://problem/15931354

Note that r271282 contains only the src change from Clang rev 200797.
This patch file includes two follow-on changes to the test case, which
do not apply to the copy in the FreeBSD tree.

Upstream Clang revisions:

200797:

    Debug info: fix a crasher when when emitting debug info for
    not-yet-completed templated types. getTypeSize() needs a complete type.

    rdar://problem/15931354

200798:

    Simplify testcase from r200797 some more.

200805:

    Further simplify r200797 and add an explanatory comment.