[libunwind] Always use unwind tables in tests

    
For many targets setting -fno-exceptions will prevent unwinding tables from
being generated for the test programs. As libunwind depends on the tables to
unwind the stack several tests will fail.

This change always adds -funwind-tables so that even when -fno-exceptions
is set unwind tables are generated.

fixes PR33858

Differential Revision: https://reviews.llvm.org/D37484

llvm-svn: 316657