[skip ci] Sync file permissions in Git repository

Git can track executable (0755) and non-executable (0644) file modes.
This is a minor file permissions sync across the php-src Git repository.

- build/config.guess (0755 as done upstream)
- build/config.sub (0755 as done upstream)
- ext/*/?*.stub.php (0644)
- ext/mbstring/libmbfl/mbfl/mk_eaw_tbl.awk (0755 due to shebang usage)

Author: petk