Previously, we relied on shell word splitting, which leads
to passing the wrong arguments when there are white spaces
in the path.
Avoiding command substitution also makes this script more
likely to work under Solaris 10, where `/bin/sh` is not
POSIX compliant [1]. (Thanks you, `@znz` for fixing the syntax
error in 4210ae2158 though!)
The hack from c466f270b8
doesn't actually work so this commit reverts it. The shell
still needs to parse through all of the code, maybe because
make doesn't in fact send newlines to the shell.
By the way, we also use the `-exec` option in the `ext/distclean` task.
[1]: https://docs.oracle.com/cd/E26505_01/html/816-5165/sh-1.html
99281f513c