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. On x86_64 clang will add this option implicitly as the ABI requires it, I've tested this with Arm and AArch64.
This is an attempt at fixing pr33858 https://bugs.llvm.org/show_bug.cgi?id=33858. I'm not experienced in this area so there may well be better ways of doing this.