Fix template class debug info for Visual Studio visualizers

An earlier change eliminated spaces between the close brackets of nested
template lists.  Unfortunately that prevents the Windows debuggers from
matching some types to their corresponding visualizers (e.g., std::map).

This selects the SeparateTemplateClosers flag when generating CodeView.
Note that we were already making formatting adjustments under similar
circumstances for similar reasons.

This wasn't caught by existing tests because they were using only
-std=c++98.

Differential Revision: https://reviews.llvm.org/D79274