Always add libdirs to rustc command

[leftmostcat]

This works around an issue in which meson provides absolute paths to rustc, but rustc may do its own dependency resolution and add -l flags for the same libs, causing a failure to link. See #14622.

[bonzini]

The idea seems acceptable, but I don't understand the if. Do you need to run the new code even if not a.endswith(('.dll', '.so', '.dylib', '.a', '.lib'))?

In other words, should this be

                if a in rustc.native_static_libs:
                    # Exclude link args that rustc already add by default
                    continue
                if a.startswith('-L'):
                    args.append(a)
                    continue
                if a.endswith(('.dll', '.so', '.dylib', '.a', '.lib')):
                    # Work around a disconnect in meson and rustc behavior in
                    # which rustc performs some dependency resolution of its own
                    # and adds `-l:our_lib` despite having an absolute path to
                    # `our_lib.a`. Always add the -L option.
                    dir_, lib = os.path.split(a)
                    linkdirs.add(dir_)
                    if isinstance(target, build.StaticLibrary):
                        if not verbatim:
                            lib, ext = os.path.splitext(lib)
                            if lib.startswith('lib'):
                                lib = lib[3:]
                        static = a.endswith(('.a', '.lib'))
                        _link_library(lib, static)
                        continue
                args.append(f'-Clink-arg={a}')

or something like that

[leftmostcat]

I've adjusted this based on the review. I've removed the comment for now as I don't really understand why these were separated previously and what's happening with static libs, so I don't want comments that make no sense for the existing context. I can add something back if there's a need.

[bonzini]

The new commit is the same as the old one.

https://github.com/mesonbuild/meson/compare/c7729a6..982988bda8243e8135659766fd0a2d40cc2cc935

[leftmostcat]

Forgot to stage. 🤦

[bonzini]

LGTM. Please add "Fixes: #14622" to the description, so that issue and pull request are linked.