There is an unfortunate limitation with default tiered policy that we would have at least 2 threads on 1 CPU machine: 1 thread for C1, and 1 thread for C2.

But if we select C1-only or C2-only modes, we _also_ get 2 compiler threads, for which we have no good reason. These threads would just step on each other toes.

$ build/linux-x86_64-server-release/images/jdk/bin/java -XX:-TieredCompilation -XX:ActiveProcessorCount=1 -XX:+PrintFlagsFinal 2>&1 | grep CICompilerCount
     intx CICompilerCount = 2 {product} {ergonomic}
     bool CICompilerCountPerCPU = true {product} {default}

$ build/linux-x86_64-server-release/images/jdk/bin/java -XX:TieredStopAtLevel=1 -XX:ActiveProcessorCount=1 -XX:+PrintFlagsFinal 2>&1 | grep CICompilerCount
     intx CICompilerCount = 2 {product} {ergonomic}
     bool CICompilerCountPerCPU = true {product} {default}

It is a minor bug in `CompilationPolicy::initialize`, but it gets in the way studying Leyden in tight CPU scenarios.