[LLGS] Limit jThreadsInfo to only the most important registers for now
It seems that reading of register data is the biggest bottleneck in LLGS at the moment. Sending
four registers instead of the full GPR set increases the jThreadsInfo processing time about
6-fold. Until we figure out where is this time going, this commit limits the amount of data we
send to provide a more fluid debugging experience.
Reviewers: tberghammer, ovyalov
Differential Revision: http://reviews.llvm.org/D11264