Merging r285703:

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r285703 | achurbanov | 2016-11-01 11:19:04 -0500 (Tue, 01 Nov 2016) | 9 lines

Fixed problem introduced by part of https://reviews.llvm.org/D21196.

Check Task Scheduling Constraint (TSC) on stealing of untied task.
This is needed because the untied task can produce tied children
those can break TSC if untied is not a descendant of current task.
This can cause live lock on complex tyasking tests
(e.g. kastors/strassen-task-dep).

Differential Revision: https://reviews.llvm.org/D26182
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llvm-svn: 287561