patch 9.0.2098: No filetype support for xcompose files

Problem:  No filetype support for xcompose files
Solution: Add filetype detection

closes: #13508

Signed-off-by: ObserverOfTime <chronobserver@disroot.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/xcompose.vim b/runtime/ftplugin/xcompose.vim
new file mode 100644
index 0000000..7345c27
--- /dev/null
+++ b/runtime/ftplugin/xcompose.vim
@@ -0,0 +1,13 @@
+" Vim filetype plugin file
+" Language:	XCompose
+" Maintainer:	ObserverOfTime <chronobserver@disroot.org
+" Last Change:	2023 Nov 09
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+setl comments=:# commentstring=#\ %s
+
+let b:undo_ftplugin = 'setl com< cms<'