abuild: add amove func to move from $pkgdir to $subpkgdir

moving files and directories from $pkgdir to $subpkgdir is a common
pattern, so make a helper function for this.

usage: amove FILESPEC...

FILESPEC is a list of files or patterns/globs that will be exanded by
the shell.

amove will clean up empty directories after moving the files/dirs.

Example usage:

  amove 'usr/lib/lib*.a'
  amove 'etc/*.d' # moves both etc/conf.d and etc/init.d
  amove 'lib/*.so' 'usr/lib/*.so'

  cd "$pkgdir"
  find usr -name '*.h' | xargs amove

This is based on the work of Chloe Kudryavtsev:
https://github.com/alpinelinux/abuild/pull/92

abuild.in

@@ -72,6 +72,29 @@ error() {
 	logcmd "ERROR: $pkgname: $1"
 }
 
+amove() {
+	[ -n "$subpkgdir" ] || return 1
+
+	# store directory
+	d="$(pwd -L)"
+
+	cd "$pkgdir"
+	local pattern f
+	for pattern; do
+		for f in ${pattern#/}; do # let shell expand the pattern
+			# only create dir if needed
+			if [ "${f%/*}" != "$f" ]; then
+				mkdir -p "$subpkgdir/${f%/*}"
+			fi
+			mv -v "$pkgdir"/$f "$subpkgdir/${f%/*}"
+			# cleanup
+			rmdir -p "$f" || rmdir -p "${f%/*}" || true
+		done
+	done
+
+	cd "$d"
+}
+
 cross_creating() {
 	test "$CHOST" != "$CTARGET" -a -n "$CBUILDROOT"
 }