Auto merge of #2396 - ivmarkov:master, r=JohnTitor

Support for the ESP-IDF framework - 3 forgotten mappings

When implementing [the initial support for ESP-IDF](#2310) a month ago, I managed to forget to properly decorate these 3 libc bindings for the ESP-IDF.

So now we are in the uncomfortable situation that using STD's `TcpListener::bind` results in a linkage error.

This PR is fixing this, as well as properly exposing two additional ESP-IDF APIs, implemented via LwIP.

src/unix/newlib/mod.rs

@@ -611,17 +611,20 @@ extern "C" {
         target_arch = "powerpc",
         target_vendor = "nintendo"
     )))]
+    #[cfg_attr(target_os = "espidf", link_name = "lwip_bind")]
     pub fn bind(fd: ::c_int, addr: *const sockaddr, len: socklen_t) -> ::c_int;
     pub fn clock_settime(clock_id: ::clockid_t, tp: *const ::timespec) -> ::c_int;
     pub fn clock_gettime(clock_id: ::clockid_t, tp: *mut ::timespec) -> ::c_int;
     pub fn clock_getres(clock_id: ::clockid_t, res: *mut ::timespec) -> ::c_int;
+    #[cfg_attr(target_os = "espidf", link_name = "lwip_close")]
     pub fn closesocket(sockfd: ::c_int) -> ::c_int;
     pub fn ioctl(fd: ::c_int, request: ::c_ulong, ...) -> ::c_int;
     #[cfg(not(all(
         libc_cfg_target_vendor,
         target_arch = "powerpc",
         target_vendor = "nintendo"
     )))]
+    #[cfg_attr(target_os = "espidf", link_name = "lwip_recvfrom")]
     pub fn recvfrom(
         fd: ::c_int,
         buf: *mut ::c_void,