Test coverage for non-default-constructible elements in a StringMap

This functionality was enabled by r198374. Here's a test to ensure it
works and we don't regress it.

Based on a patch by Maciej Piechotka.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198377 91177308-0d34-0410-b5e6-96231b3b80d8
Fix break introduced in r198377 due to using a local type as a template parameter.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198379 91177308-0d34-0410-b5e6-96231b3b80d8
Reverting r193835 due to weirdness with Go...

Apologies for the noise - we're seeing some Go failures with cgo
interacting with Clang's debug info due to this change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198385 91177308-0d34-0410-b5e6-96231b3b80d8