[modules] Fix deserialization cycle when loading a tag declaration with a typedef...

[modules] Fix deserialization cycle when loading a tag declaration with a typedef name for linkage purposes. When loading the type, delay loading its typedef until we've finished loading and merging the type. In its place, save out the name of the typedef, which we need for merging purposes.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216806 91177308-0d34-0410-b5e6-96231b3b80d8