Enable usage of eh_frame based unwind plan as a fallback

Previously if the instruction emulation based unwind plan failed then
we fall back to the arch default unwind plan. Change it to fall back
to the eh_frame based one even on non call sites if we have eh_frame
as that one tend to be more reliable.

Differential revision: http://reviews.llvm.org/D10902

llvm-svn: 241334