Generate a callsite identifier associated with each callsite

1. Generate a unique string name for a callsite that appears in every node
2. This identifier will refer to a single callsite and is used for trace data retrieval

@ke-yu
@lukechurch
@Steell
@Benglin

Don't use this style please. Developers who were born after C++ won't get it.

In this case:
b++;
a = b;