libunwind is not yet ported for ARC & RISCV64 and on attempt
to build it for those arches we just get an error message.
If we explicitly disable libunwind it is gracefully handled by
perf build system and it just gets configured to not use it
so perf is still usable even on those arches.
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com> Cc: Khem Raj <raj.khem@gmail.com> Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
