Adding compact unwind as a source of unwind information

introduced subtle bugs in two places in 
RegisterContextLLDB::GetFullUnwindPlanForFrame where 
it specifically wanted to get an eh_frame unwind plan
and was using "Get CallSite UnwindPlan" as synonymous
with that.  But now we have two different types of 
unwind plan that can be returned in that case, and
compact unwind won't behaves as needed.

<rdar://problem/19528559> 

llvm-svn: 226631