Add test for ioctl(SIOCGIFCONF) and polyfill on BSDs

- Use nullness checks when calling weakly linked functions.

- Avoid typedef for reasons described in Linux Kernel style guide.

- Avoid enum in in Windows headers. Earlier in Cosmo's history all one
  hundred files in libc/nt/enum/ used to be enums and it resulted in
  gigabytes of DWARF data almost as large as everything else in the
  codebase combined.

- Bitfields aren't our friends. They have frequent ABI breakages,
  inconsistent arithmetic across compilers, and different endianness
  between cpus. Compiler authors also haven't invested much roi into
  making bit fields go fast so they produce poor assembly.

- Use memccpy() instead of strncpy() or snprintf() for length-bounded
  copying of C strings. strncpy() is a misunderstood function and
  snprintf() is awesome but memccpy() deserves more love.

libc/sock/internal.h

@@ -53,45 +53,8 @@ struct sockaddr_un_bsd {
   char sun_path[108];
 };
 
-/* -----------------------------------------------------------------------------------
- * ioctl SIOCGIFCONF & others:
- *
- * BSD has a different structure. All the ioctl will adjust to use
- * the ifreq with the ifreq_bsd
- */
-struct ifreq_bsd {
-  union {
-    char ifrn_name[IFNAMSIZ];
-  } ifr_ifrn;
-
-  union {
-    /* Right now we only list the structures used by the few ioctl that are
-     * supported by Cosmopolitan. Add your own definition here if you need
-     * a particular ioctl that requires polyfill for BSD
-     */
-    struct  sockaddr_bsd ifru_addr;
-    struct  sockaddr_bsd ifru_netmask;
-    struct  sockaddr_bsd ifru_dstaddr;
-    struct  sockaddr_bsd ifru_broadaddr;
-    short   ifru_flags;
-    char    ifru_pad[16];   /* used as padding */
-  } ifr_ifru;
-};
-
-#pragma pack(4)
-struct ifconf_bsd {
-  uint32_t ifc_len;            /* size of buffer   */
-  union {
-    char *ifcu_buf;
-    struct ifreq_bsd *ifcu_req;
-  } ifc_ifcu;
-};
-#pragma pack()
-
-
 /* ------------------------------------------------------------------------------------*/
 
-
 struct SockFd {
   int family;
   int type;