fix: detecting windows root paths with unix-style separators

[quanterion]

On Windows Clang can produce DWARF debug information containing paths to DW_AT_name and DW_AT_comp_dir with unix-stlye slashes. for example C:/myproject/main.cpp. In that case case addr2line mistakenly concatenating absolute path to file with compilation directory

[quanterion]

@philipc can have a look at PR please?

[philipc]

Seems fine but I would like to do some testing and don't currently have time.

[quanterion]

ok, feel free to ping me if I can help you

[philipc]

This function is used for two purposes: to determine if a path is a root path, and to determine which separator to use. If the root path is using :/, then I think we also be using / for the separator, but that won't happen with this change. Perhaps this change should be in has_unix_root instead. After doing that, better names for these functions would be has_forward_slash_root and has_backward_slash_root.

[philipc]

It would help with testing this if you can add a test file to https://github.com/gimli-rs/object-testfiles/tree/master/dwarf (ideally it would be the base.cpp in that directory compiled with clang on Windows).

[quanterion]

@philipc refactored the code and here is the branch with clang binary from windows gimli-rs/object-testfiles#22