This doesn't add support for the legacy symbol mangling scheme which is
currently the default pending support in tools for the v0 symbol
mangling scheme. The legacy symbol mangling scheme is similar enough to
C++'s symbol mangling scheme that demangling them using the C++
demangler generally produces readable symbols. The v0 scheme is entirely
custom and due to backreferences and encoding all generic arguments not
very readable when mangled, so supporting it is more important than
supporting the legacy scheme.
This brings together the two libraries back into one now that the whole
design is pretty well sorted out. They depend on roughly the same libraries
anyway and it's way easier of the single library can both read and write
the capture files (along with bringing in libsysprof-capture symbols in
a single place).
