Increase the size of this SmallVector in CloneNodeWithValues.

In a Clang bootstrap, the size of this vector was always 6.
Increase the size of these SmallVectors in X86ISelLowering.cpp.

In a Clang bootstrap, their sizes were always 12, 16 and 16, respectively.
LegacyPassManagers.h: increase the size of PMDataManager::HigherLevelAnalysis.

In a Clang bootstrap, the median and max size was 9.
Increase the size of SpillPlacement::BlockFrequencies.

This SmallVector's median size during a Clang build was 7.
SubTargetFeature.cpp: it seems the size of this SmallVector should be 3

because some subtarget feature strings have three components.
Increase the size of this SmallVector in PeepholeOptimizer.

During a Clang build, the median size of this was 9