libglnx porting: Use glnx_set_error_from_errno

⚠️ There is a notable spiked pit trap here around
`posix_fallocate()` and `errno`.  This has bit other projects,
see e.g.
https://github.com/systemd/systemd/commit/7bb87460e691d30c1a7fd23a1a8240776957e05f

Otherwise the port was straightforward.

src/libostree/ostree-repo-static-delta-compilation.c

@@ -465,7 +465,7 @@ get_unpacked_unlinked_content (OstreeRepo       *repo,
   fd = g_mkstemp (tmpname);
   if (fd == -1)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
   /* Doesn't need a name */