There's a merged pull request on the void-packages repository

xbps-src: correctly cleanup masterdir/tmp in the 'clean' target
https://github.com/void-linux/void-packages/pull/19513

Description:
465e481b70a forgot `rm -r` when cleaning /tmp. 
As a result, `xbps-src clean` returned 1 when directories were present in /tmp
because rm returned with an (suppressed) error.

Also use the global variables for builddir and destdir, to be more consistent.