Fix new noreturn test on !darwin platforms

r221575 introduced a NoreturnUnwind test that did not skip the dsym
test on non-darwin platforms, and had the @dwarf_test case as an exact
copy of the dsym case (including the test name, test_with_dsym).


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@221611 91177308-0d34-0410-b5e6-96231b3b80d8