make CHECK_FUNC_GETADDRINFO_UNFREEABLE_AI_ADDR
and CHECK_FUNC_GETADDRINFO_UNFREEABLE_AI_CANONNAME
internal to CHECK_FUNC_GETADDRINFO

fix leftover

Initial attempt to detect at configuration time if the getaddrinfo()
function returns an addrinfo with an unfreeable ai_canonname member ptr.

Initial attempt to detect at configuration time if the getaddrinfo()
function returns an addrinfo with an unfreeable ai_addr member ptr.

Raise message severity up to warning, when strerror_r() exists but
configure is unable of finding out if it has glibc-style or POSIX-style,
trying to ensure that this condition does not go un

Raise message severity up to warning, when strerror_r() exists but
configure is unable of finding out if it has glibc-style or POSIX-style,
trying to ensure that this condition does not go unnoticed.

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#include <stdlib.h> for exit() prototype

siginterrupt, signal and sigsetjmp checks

HAVE_INET_PTON will only be defined when an IPv6 capable working
inet_pton function is available.

configure script now checks availability of the inet_ntop() function,
and when not crosscompiling verifies if it is IPv6 capable.

HAVE_INET_NTOP will only be defined when an IPv6 capable

configure script now checks availability of the inet_ntop() function,
and when not crosscompiling verifies if it is IPv6 capable.

HAVE_INET_NTOP will only be defined when an IPv6 capable working
inet_ntop function is available.

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temporarily enable CURL_CHECK_FUNC_INET_NTOA_R

attempt to make work the gethostname function
check for winsock build target configurations

configure script now checks availability of the alarm() function

fix false negative strerror_r detection

fix wrong number used in comparison

fix wrong variable used in comparison

fix netdb.h prerequisite inclusion

improve detection of gethostbyaddr_r() and gethostbyname_r()

improve detection of getservbyport_r()

improve detection of gethostname(), localtime_r() and strstr()

rearrange to allow internal/private use of ares_writev to any system
that lacks the writev function.

remove debug tracing

improve detection of:
strcasecmp()
strcasestr()
strcmpi()
stricmp()
strlcat()
strncasecmp()
strncmpi()
strnicmp()

also check for an 'unsigned int' for third argument of strerror_r()

improve detection of strerror_r()

add some debug tracing