CalcSpillWeights: Hack to prevent x87 nonsense

This gross hack forces `hweight` into memory, preventing hidden
precision from making `1 > 1` occasionally equal `true`.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206765 91177308-0d34-0410-b5e6-96231b3b80d8
Reapply "blockfreq: Rewrite BlockFrequencyInfoImpl"

This reverts commit r206707, reapplying r206704.  The preceding commit
to CalcSpillWeights should have sorted out the failing buildbots.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206766 91177308-0d34-0410-b5e6-96231b3b80d8