[MS] Fix late-parsed template infinite loop in eager instantiation

[MS] Fix late-parsed template infinite loop in eager instantiation

Summary:
This fixes PR33561 and PR34185.

Don't store pending template instantiations for late-parsed templates in
the normal PendingInstantiations queue. Instead, use a separate list
that will only be parsed and instantiated at end of TU when late
template parsing actually works and doesn't infinite loop.

Reviewers: rsmith, thakis, hans

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D44846

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@328567 91177308-0d34-0410-b5e6-96231b3b80d8