patch 8.0.0451: some macros are in lower case

Problem:    Some macros are in lower case.
Solution:   Make a few more macros upper case. Avoid lower case macros use an
            argument twice.
diff --git a/src/fold.c b/src/fold.c
index db8da63..9597ab8 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -2064,7 +2064,7 @@
 	}
 	else
 	{
-	    mb_ptr_adv(s);
+	    MB_PTR_ADV(s);
 	}
     }
 }
@@ -3249,7 +3249,7 @@
 		--flp->lvl_next;
 	}
 	else
-	    mb_ptr_adv(s);
+	    MB_PTR_ADV(s);
     }
 
     /* The level can't go negative, must be missing a start marker. */