Fixes#9044, close#9667. Thanks to @taku0 for suggesting this solution.
Now we have no modes starting with `/` or `+`.
Rewrite the `-perm` parameters of find:
- completely safe: rewrite `/0100` and `+100` to `-0100`,
- slightly semantics-changing: rewrite `+111` to `-0100`.
I cross-verified the `find` manual pages for Linux, Darwin, FreeBSD.
The script does a copy of a toolchain and then rearranges files a bit.
The problem is that these files have the same permissions (read-only)
as installed ones. The patch fixes the problem by changing permissions
of the copy before doing anything else.
