Fixes potential hang in accept by using select + non-blocking accept.
Fixes potential hang in peer check by replacing the send/recv check with
a getsockname/getpeername check.
Adds length check for returned sockaddr data.
Closes#7144
- Undefine DEBUGASSERT in curl_setup_once.h in case it was already
defined as a system macro.
- Don't compile write32_le in curl_endian unless
CURL_SIZEOF_CURL_OFF_T > 4, since it's only used by Curl_write64_le.
- Include <arpa/inet.h> in socketpair.c.
Closes https://github.com/curl/curl/pull/4756
