patch 8.0.1723: using one item array size declaration is misleading

Problem:    Using one item array size declaration is misleading.
Solution:   Instead of using "[1]" and actually using a larger array, use
            "[]".  This is to verify that this C99 feature works for all
            compilers.
diff --git a/src/structs.h b/src/structs.h
index d3f98ac..9202527 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -511,7 +511,7 @@
 struct buffblock
 {
     buffblock_T	*b_next;	/* pointer to next buffblock */
-    char_u	b_str[1];	/* contents (actually longer) */
+    char_u	b_str[];	/* contents (flexible array) */
 };
 
 /*
@@ -519,7 +519,7 @@
  */
 struct buffheader
 {
-    buffblock_T	bh_first;	/* first (dummy) block of list */
+    buffblock_T	*bh_first;	/* first block of the list */
     buffblock_T	*bh_curr;	/* buffblock for appending */
     int		bh_index;	/* index for reading */
     int		bh_space;	/* space in bh_curr for appending */