While for Swift symbols, they always exist in the module streams, the
PDBs that Microsoft serves from its symbol servers don't work that
way, and contain symbols that don't show up in the module streams.
Thus we need to add function data for each of those.
That then creates a problem where the symbol is in both places, so we
need to de-duplicate as well.
rdar://176547291
Without scanning the main symbol stream, we get weird names for the
Swift functions in the backtrace, because the compiler generates C++-style
names for them. We actually want the mangled names, if possible, which
only seem to be in the symbol stream, so scan that as well and use it
to find mangled names.
rdar://168454023
Alastair Houghton
Allan Shortlidge