patch 9.0.0951: trying every character position for a match is inefficient

Problem:    Trying every character position for a match is inefficient.
Solution:   Use the start position of the match ignoring "\zs".

src/regexp.h

@@ -133,6 +133,8 @@ typedef struct
     regprog_T		*regprog;
     char_u		*startp[NSUBEXP];
     char_u		*endp[NSUBEXP];
+
+    colnr_T		rm_matchcol;   // match start without "\zs"
     int			rm_ic;
 } regmatch_T;
 
@@ -149,6 +151,8 @@ typedef struct
     regprog_T		*regprog;
     lpos_T		startpos[NSUBEXP];
     lpos_T		endpos[NSUBEXP];
+
+    colnr_T		rmm_matchcol;   // match start without "\zs"
     int			rmm_ic;
     colnr_T		rmm_maxcol;	// when not zero: maximum column
 } regmmatch_T;