Eliminate the use of PriorityQueue and just use a std::vector,

Eliminate the use of PriorityQueue and just use a std::vector,
implementing pop with a linear search for a "best" element. The priority
queue was a neat idea, but in practice the comparison functions depend
on dynamic information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104718 91177308-0d34-0410-b5e6-96231b3b80d8