[ELF] - Add testcase for -debugger-tune=<value>

In D42733 we supported different LTO command line
options, including -debugger-tune=<value>.

Initially debugger-tune support was needed to fix PR36035.
Patch adds testcase for this option to check we
don't simply ignore it.

Differential revision: https://reviews.llvm.org/D42961

llvm-svn: 324457