patch 8.1.2389: using old C style comments

Problem:    Using old C style comments.
Solution:   Use // comments where appropriate.
diff --git a/src/xdiff/xdiff.h b/src/xdiff/xdiff.h
index 783dc9d..3dc9520 100644
--- a/src/xdiff/xdiff.h
+++ b/src/xdiff/xdiff.h
@@ -25,9 +25,9 @@
 
 #ifdef __cplusplus
 extern "C" {
-#endif /* #ifdef __cplusplus */
+#endif // #ifdef __cplusplus
 
-/* xpparm_t.flags */
+// xpparm_t.flags
 #define XDF_NEED_MINIMAL (1 << 0)
 
 #define XDF_IGNORE_WHITESPACE (1 << 1)
@@ -48,22 +48,22 @@
 
 #define XDF_INDENT_HEURISTIC (1 << 23)
 
-/* xdemitconf_t.flags */
+// xdemitconf_t.flags
 #define XDL_EMIT_FUNCNAMES (1 << 0)
 #define XDL_EMIT_FUNCCONTEXT (1 << 2)
 
-/* merge simplification levels */
+// merge simplification levels
 #define XDL_MERGE_MINIMAL 0
 #define XDL_MERGE_EAGER 1
 #define XDL_MERGE_ZEALOUS 2
 #define XDL_MERGE_ZEALOUS_ALNUM 3
 
-/* merge favor modes */
+// merge favor modes
 #define XDL_MERGE_FAVOR_OURS 1
 #define XDL_MERGE_FAVOR_THEIRS 2
 #define XDL_MERGE_FAVOR_UNION 3
 
-/* merge output styles */
+// merge output styles
 #define XDL_MERGE_DIFF3 1
 
 typedef struct s_mmfile {
@@ -79,7 +79,7 @@
 typedef struct s_xpparam {
 	unsigned long flags;
 
-	/* See Documentation/diff-options.txt. */
+	// See Documentation/diff-options.txt.
 	char **anchors;
 	size_t anchors_nr;
 } xpparam_t;
@@ -130,9 +130,9 @@
 	int level;
 	int favor;
 	int style;
-	const char *ancestor;	/* label for orig */
-	const char *file1;	/* label for mf1 */
-	const char *file2;	/* label for mf2 */
+	const char *ancestor;	// label for orig
+	const char *file1;	// label for mf1
+	const char *file2;	// label for mf2
 } xmparam_t;
 
 #define DEFAULT_CONFLICT_MARKER_SIZE 7
@@ -142,6 +142,6 @@
 
 #ifdef __cplusplus
 }
-#endif /* #ifdef __cplusplus */
+#endif // #ifdef __cplusplus
 
-#endif /* #if !defined(XDIFF_H) */
+#endif // #if !defined(XDIFF_H)