Module debug info: Fix a bug in handling record decls without fields.

The previous condition would erroneously mark all CXXRecordDecls
that didn't have any fields as being defined in a clang module.
This patch fixes the condition to only apply to explicit template
instantiations.

<rdar://problem/27771823>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@278952 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit db4c239f5ed8cdf4a0b886c2b18ccb8621f85230)
4 files changed