Change LiveStackAnalysis::SS2IntervalMap from std::map to std::unordered_map

This use case doesn't appear to benefit from ordering, and
std::unordered_map has the advantage that it supports emplace (the
LiveInterval values really shouldn't be copyable or movable & they won't
be in a near-future patch).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231175 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed