DebugInfo: Emit function definitions within their namespace scope.

This workaround (presumably for ancient GDB) doesn't appear to be
required (GDB 7.5 seems to tolerate function definition DIEs in
namespace scope just fine).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209189 91177308-0d34-0410-b5e6-96231b3b80d8