Attached warnings from clang 7.0 when compiling child-wait.c from dovecot 2.3.5:

"arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension

[-Wnull-pointer-arithmetic]".

This is fixed in master with

https://github.com/dovecot/core/commit/ac7aa955db4c77bbb169baa5d104a4c128674646.patch