MDEV-4425 REGEXP enhancements

Adding pcre_stack_guard to avoid crashes in pcre_compile()
on a long recursive patterns with parenthesizes:

SELECT a RLIKE '((((...((((x)))...))))';

pcre/pcre_compile.c

@@ -7107,6 +7107,12 @@ unsigned int orig_bracount;
 unsigned int max_bracount;
 branch_chain bc;
 
+if (pcre_stack_guard && pcre_stack_guard())
+{
+  *errorcodeptr= ERR23;
+  return FALSE;
+}
+ 
 bc.outer = bcptr;
 bc.current_branch = code;