Fix multiple problems of lldb-mi blocking on input monitoring and needing a return.

Summary:
One of the problem is reported here.
http://llvm.org/bugs/show_bug.cgi?id=22411

A fix was committed for this problem that works only for OSX. This revision
extends that fix to other system. The select system call has some limitation with
multi-threaded application which have been addresses here.

LLDB-mi exits if quit command is given but needs an extra retur if -gdb-exit is
given. That issue has also been addressed.

Reviewers: ki.stfu, emaste

Reviewed By: ki.stfu

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D7529

llvm-svn: 228709