patch 8.2.3969: value of MAXCOL not available in Vim script

Problem:    Value of MAXCOL not available in Vim script.
Solution:   Add v:maxcol. (Naohiro Ono, closes #9451)
diff --git a/src/evalvars.c b/src/evalvars.c
index 324355b..ea98861 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -154,6 +154,7 @@
     {VV_NAME("sizeofint",	 VAR_NUMBER), NULL, VV_RO},
     {VV_NAME("sizeoflong",	 VAR_NUMBER), NULL, VV_RO},
     {VV_NAME("sizeofpointer",	 VAR_NUMBER), NULL, VV_RO},
+    {VV_NAME("maxcol",		 VAR_NUMBER), NULL, VV_RO},
 };
 
 // shorthand
@@ -241,6 +242,7 @@
     set_vim_var_nr(VV_SIZEOFINT, sizeof(int));
     set_vim_var_nr(VV_SIZEOFLONG, sizeof(long));
     set_vim_var_nr(VV_SIZEOFPOINTER, sizeof(char *));
+    set_vim_var_nr(VV_MAXCOL, MAXCOL);
 
     set_vim_var_nr(VV_TYPE_NUMBER,  VAR_TYPE_NUMBER);
     set_vim_var_nr(VV_TYPE_STRING,  VAR_TYPE_STRING);