patch 8.1.2368: using old C style comments

Problem:    Using old C style comments.
Solution:   Use // comments where appropriate.
diff --git a/src/blob.c b/src/blob.c
index 278ced6..2a7ec3a 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -328,4 +328,4 @@
     }
 }
 
-#endif /* defined(FEAT_EVAL) */
+#endif // defined(FEAT_EVAL)