[lldb comparator] ability to execute in parallel

[Vipul-Cariappa]

LLDBDebugger handles only 1 lldb instance (similar to IDDGdbController)
LLDBParallelDebugger handles 2 instance of LLDBDebugger and is responsible for parallel execution

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Works similar to #29

Test with

// main.c

#include<unistd.h>

int main() {
    sleep(5); // sleep for 5 secs
    return 1;
}

Previously it would take ~10.5 secs. Now it takes ~5.5 secs.