Auto merge of #2485 - DimitrisJim:freebsd_ai_consts, r=Amanieu

Add AI_* constants to freebdslike platforms.

For dragonfly, some of the constants (`AI_MASK`, `AI_V4MAPPED_CFG` and `AI_DEFAULT`) are behind a `__BSD_VISIBLE` define. What's the best way to handle these?

Header files for [dragonfly](https://git.quantumachine.net/mirror/DragonFlyBSD/src/branch/master/include/netdb.h) and [freebsd](https://cgit.freebsd.org/src/tree/include/netdb.h).

For now, I've just added all common names to `freebdslike`.

Author: bors

libc-test/semver/freebsd.txt

@@ -55,6 +55,13 @@ AIO_ALLDONE
 AIO_CANCELED
 AIO_LISTIO_MAX
 AIO_NOTCANCELED
+AI_PASSIVE
+AI_CANONNAME
+AI_NUMERICHOST
+AI_NUMERICSERV
+AI_ALL
+AI_ADDRCONFIG
+AI_V4MAPPED
 ALTMON_1
 ALTMON_10
 ALTMON_11

src/unix/bsd/freebsdlike/mod.rs

@@ -724,6 +724,14 @@ pub const POLLSTANDARD: ::c_short = ::POLLIN
     | ::POLLHUP
     | ::POLLNVAL;
 
+pub const AI_PASSIVE: ::c_int = 0x00000001;
+pub const AI_CANONNAME: ::c_int = 0x00000002;
+pub const AI_NUMERICHOST: ::c_int = 0x00000004;
+pub const AI_NUMERICSERV: ::c_int = 0x00000008;
+pub const AI_ALL: ::c_int = 0x00000100;
+pub const AI_ADDRCONFIG: ::c_int = 0x00000400;
+pub const AI_V4MAPPED: ::c_int = 0x00000800;
+
 pub const EAI_AGAIN: ::c_int = 2;
 pub const EAI_BADFLAGS: ::c_int = 3;
 pub const EAI_FAIL: ::c_int = 4;