xbps-src: replace basename(1) with ${var##*/}.

Reduce number of fork+exec due to using a subshell to execute basename(1).

common/xbps-src/shutils/purge_distfiles.sh

@@ -75,7 +75,7 @@ purge_distfiles() {
 	hashes=($XBPS_SRCDISTDIR/by_sha256/*)
 	readonly HASHLEN=64
 	for file in ${hashes[@]}; do
-		hash_distfile=$(basename "$file")
+		hash_distfile=${file##*/}
 		hash=${hash_distfile:0:$HASHLEN}
 		[ -n "${my_hashes[$hash]}" ] && continue
 		inode=$(stat "$file" --printf "%i")