[llvm-cxxfilt][macOS] Don't strip underscores on macOS by default (#106233)

Currently, `llvm-cxxfilt` will strip the leading underscore of its input
on macOS. Historically MachO symbols were prefixed with an extra
underscore and this is why this default exists. However, nowadays, the
`ItaniumDemangler` supports all of the following mangling prefixes:
`_Z`, `__Z`, `___Z`, `____Z`. So really `llvm-cxxfilt` can simply
forward the mangled name to the demangler and let the library decide
whether it's a valid encoding.

Compiling C++ on macOS nowadays will generate symbols with `_Z` and
`___Z` prefixes. So users trying to demangle these symbols will have to
know that they need to add the `-n` prefix. This routinely catches
people off-guard.

This patch removes the `-n` default for macOS and allows calling into
the `ItaniumDemangler` with all the `_Z` prefixes that the demangler
supports (1-4 underscores).

rdar://132714940

0 files changed, 0 insertions, 0 deletions