[clang] [llvm] [ImmutableSet] Optimize add/remove operations to avoid redundant tree modifications (PR #159845)

[Gábor Horváth via llvm-commits]

Xazax-hun wrote:

cc., @steakhal , @necto , @NagyDonat , you might want to run some benchmarks with this patch applied to see if there is a measurable impact on the Clang Static Analyzer. 

https://github.com/llvm/llvm-project/pull/159845