abuild: run build actions via runpart

So we make sure chdir $builddir happens when it should.

abuild.in

@@ -1508,7 +1508,7 @@ create_apks() {
 }
 
 build_abuildrepo() {
-	local _check=check
+	local part _check=check
 	if options_has "checkroot"; then
 		_check=check_fakeroot
 	fi
@@ -1520,16 +1520,10 @@ build_abuildrepo() {
 		abuild-sign --installed
 		logcmd "building $repo/$pkgname-$pkgver-r$pkgrel"
 		msg "Building $repo/$pkgname $pkgver-r$pkgrel (using $program $program_version)"
-		sanitycheck
-		builddeps
-		clean
-		fetch
-		unpack
-		prepare
-		mkusers
-		build
-		$_check
-		rootpkg
+		for part in sanitycheck builddeps clean fetch unpack prepare mkusers build \
+				$_check rootpkg; do
+			runpart $part
+		done
 		cleanup $CLEANUP
 	fi
 	update_abuildrepo_index