Debug information is read lazily so a lot of the state of the reader
is constructred incrementally. There's also nothing preventing symbol
queries to be performed at the same time by multiple threads. This
lead to a series of crashes where the data structures used for
bookkeeping got corrupted because of concurrent modification.
This patch uses a brute-force approach where every such data-structure
got converted to a thread-safe version. I'm happy to discuss
alternatives, and also to hear ideas about whatever preformance testing
I can do to asses the impact of this patch.