patch 9.1.0432: Ancient XPM preprocessor hack may cause build errors

Problem:  Ancient XPM preprocessor hack may cause build errors.
Solution: Simplify XPM includes and get rid of complicated #ifdef magic
          (Drew Vogel).

closes: #14816

Signed-off-by: Drew Vogel <dvogel@github>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/vim32x32.xpm b/runtime/vim32x32.xpm
index 43a3a40..017b93b 100644
--- a/runtime/vim32x32.xpm
+++ b/runtime/vim32x32.xpm
@@ -1,5 +1,5 @@
 /* XPM */
-static char * vim32x32[] = {
+static const char * vim32x32[] = {
 "32 32 8 1",
 " 	c None",
 ".	c #000000",