[lldb] Pass the target triple when determining the DWARF version

When targeting iOS, the default dwarf version is 2 and not 4. Currently,
the test suite does not pick up on that because it invokes the test
compiler without a target triple. This patch fixes that and now
correctly skips tests that have a dwarf version specified in a skipIf
decorator.

rdar://84530477

Differential revision: https://reviews.llvm.org/D112325