patch 9.0.0620: matchaddpos() can only add up to 8 matches

Problem:    matchaddpos() can only add up to 8 matches.
Solution:   Allocate the array of positions. (closes #11248)

src/structs.h

@@ -3424,9 +3424,6 @@ typedef struct
 			    // CurSearch
 } match_T;
 
-// number of positions supported by matchaddpos()
-#define MAXPOSMATCH 8
-
 /*
  * Same as lpos_T, but with additional field len.
  */
@@ -3438,35 +3435,31 @@ typedef struct
 } llpos_T;
 
 /*
- * posmatch_T provides an array for storing match items for matchaddpos()
- * function.
- */
-typedef struct posmatch posmatch_T;
-struct posmatch
-{
-    llpos_T	pos[MAXPOSMATCH];	// array of positions
-    int		cur;			// internal position counter
-    linenr_T	toplnum;		// top buffer line
-    linenr_T	botlnum;		// bottom buffer line
-};
-
-/*
- * matchitem_T provides a linked list for storing match items for ":match" and
- * the match functions.
+ * matchitem_T provides a linked list for storing match items for ":match",
+ * matchadd() and matchaddpos().
  */
 typedef struct matchitem matchitem_T;
 struct matchitem
 {
-    matchitem_T	*next;
-    int		id;	    // match ID
-    int		priority;   // match priority
-    char_u	*pattern;   // pattern to highlight
-    regmmatch_T	match;	    // regexp program for pattern
-    posmatch_T	pos;	    // position matches
-    match_T	hl;	    // struct for doing the actual highlighting
-    int		hlg_id;	    // highlight group ID
+    matchitem_T	*mit_next;
+    int		mit_id;		// match ID
+    int		mit_priority;   // match priority
+
+    // Either a pattern is defined (mit_pattern is not NUL) or a list of
+    // positions is given (mit_pos is not NULL and mit_pos_count > 0).
+    char_u	*mit_pattern;   // pattern to highlight
+    regmmatch_T	mit_match;	// regexp program for pattern
+
+    llpos_T	*mit_pos_array;	// array of positions
+    int		mit_pos_count;	// nr of entries in mit_pos
+    int		mit_pos_cur;	// internal position counter
+    linenr_T	mit_toplnum;	// top buffer line
+    linenr_T	mit_botlnum;	// bottom buffer line
+
+    match_T	mit_hl;		// struct for doing the actual highlighting
+    int		mit_hlg_id;	// highlight group ID
 #ifdef FEAT_CONCEAL
-    int		conceal_char; // cchar for Conceal highlighting
+    int		mit_conceal_char; // cchar for Conceal highlighting
 #endif
 };