rmdir: throw an error if operation fails and nargout == 0 (bug #57830). * dirfns.cc (Frmdir): Change DEFMETHODX macro invocation to include nargout variable. Check nargout, and for cases where "nargout == 0" and "status" indicates failure, throw an error. For cases where "nargout > 0", return 3-value octave_value_list in variable "retval". * file-io.cc, gzip.cc, dir.m, isfolder.m, mkdir.m, run.m, tar.m, unpack.m, zip.m, pathdef.m, savepath.m, configure_make.m, install.m, uninstall.m, getpref.m, setpref.m, pkg.tst, publish.tst, system.tst: Change calls from "rmdir" to "sts = rmdir" so that an error is not unecessarily thrown in BIST tests and other clean up code.

--- a/libinterp/corefcn/file-io.cc	Mon Feb 17 20:02:10 2020 -0800
+++ b/libinterp/corefcn/file-io.cc	Mon Feb 17 20:02:18 2020 -0800
@@ -2890,7 +2890,7 @@
 %!   assert (tmpdir, tmp_tmpdir);
 %!   assert (tmpfname (1:4), "file");
 %! unwind_protect_cleanup
-%!   rmdir (tmp_tmpdir);
+%!   sts = rmdir (tmp_tmpdir);
 %!   for i = 1:numel (envvar)
 %!     if (isempty (envdir{i}))
 %!       unsetenv (envvar{i});