Check if getaddrinfo is threadsafe when function check allows it to be used

Check for basename() is now done the same as other function checks

Added check for memrchr function or macro

renamed generated config.h to curl_config.h in order to avoid clashes when libcurl is used with other projects which also have a config.h.

Refactor how libraries are checked for connect() function,
and check for connect() as it is done for other functions.

add CloseSocket camel case function check

socket() and closesocket() prototypes might be in socket.h

check for socket() and closesocket() as it is done for other functions

Moved CURL_INCLUDES_INTTYPES to curl-functions.m4 along with other CURL_INCLUDES_*

Initial step towards a configure time curl_socklen_t definition

check for poll() as it is done for other functions

Make checking for struct ifreq a prerequisite for setting
HAVE_IOCTL_SIOCGIFADDR since it's needed to use SIOCGIFADDR and Watcom C
doesn't currently define it.

check for gethostbyaddr and gethostbyname as it is done for other functions

Make configure script check if ioctl with the SIOCGIFADDR command can be
used, and define HAVE_IOCTL_SIOCGIFADDR if appropriate.

fix leftover from previous commit

fix inet_pton() runtime configure check

fix typo affecting inclusion of <arpa/inet.h> in configure
checks for inet_ntoa_r() inet_ntop() and inet_pton()

#include <string.h> in the getaddrinfo() runtime check for the memset() prototype

fix symbol definition check for fcntl.h inclusion

#include <stdlib.h> in the getifaddrs() runtime check for the exit() prototype

Refactor configure script detection of functions used to set sockets into
non-blocking mode, and decouple function detection from function capability.

check for getifaddrs and freeifaddrs as it is done for other functions

check for freeaddrinfo() at configuration phase

update aclocal file serial number

remove verification of the freeability of the addrinfo struct pointer members