[DWARF] Fix dwarf5-index-is-used.cpp
[DWARF] Fix dwarf5-index-is-used.cpp

Summary:
`dwarf5-index-is-used.cpp` have been failing after rL340206, because `clang`
have stopped to emit pubnames by default after that change. Current patch adds
`-gpubnames` option to the `clang` command line in the test to emit pubnames.

Reviewers: labath, dblaikie

Reviewed By: labath

Subscribers: clayborg, probinson, teemperor, lldb-commits, aprantl, JDevlieghere, abidh, stella.stamenova

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D51208

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@341296 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb