This fixes an issue were some LibDebug objects (for example,
Dwarf::CompilationUnit) held a reference to their parent
Dwarf::DwarfInfo object, which was constructed on the stack and later
moved to the heap.
Process-separated symbolication was cute, but ultimately the threat
model is kinda silly. We're already *running* the binary, but we're
afraid to parse its symbol table? :^)
This commit makes SystemMonitor and bt do symbolication in-process.
SymbolServer and the symbol user will be removed separately.
