ares_timeout.c: fix compiler warning
setup_once.h: HP-UX specific TRUE and FALSE definitions

Some HP-UX system headers require TRUE defined to 1 and FALSE to 0.
Header inclusion clean-up

Remove header inclusions already done in setup_once.h
setup_once.h: refactor inclusion of <unistd.h> and <sys/socket.h>

Inclusion of these two header files now done in setup_once.h
setup_once.h: HP-UX <sys/socket.h> issue workaround

Issue: When building a 32bit target with large file support HP-UX
<sys/socket.h> header file may simultaneously provide two different
sets of declarations for sendfile and sendpath functions, one with
static and another with external linkage. Given that we do not use
mentioned functions we really don't care which linkage is the
appropriate one, but on the other hand, the double declaration emmits
warnings when using the HP-UX compiler and errors when using modern
gcc versions resulting in fatal compilation errors.

Mentioned issue is now fixed as long as we don't use sendfile nor
sendpath functions.
cares-functions.m4: update thread-safeness detection of getaddrinfo()

Take in account that POSIX standard Issue 7 drops h_errno support. Now, we also
consider getaddrinfo() to be thread-safe when (_POSIX_C_SOURCE >= 200809L) or
(_XOPEN_SOURCE >= 700) independently of whether h_errno exists or not.

Take in account that h_errno might be a modifiable lvalue not defined as
a C preprocessor macro.
cares-functions.m4: add gethostname arg 2 data type check and definition
configure: check if compiler halts on function prototype mismatch
setup_once.h: HP-UX specific 'bool', 'false' and 'true' definitions.

Also reverts commit bceb40095a
cares-functions.m4: improve gethostname arg 2 data type check
vc6cares.dsp: add ares_create_query.c and ares_parse_soa_reply.c
ares_private.h: use curl_memdebug.h instead of memdebug.h
cares-override.m4: provide AC_CONFIG_MACRO_DIR definition conditionally

Provide a 'traceable' AC_CONFIG_MACRO_DIR definition only when using
an autoconf version that does not provide it, instead of what we were
doing up to now of providing and overriding AC_CONFIG_MACRO_DIR for
all autoconf versions.
configure.ac: replace AM_CONFIG_HEADER with AC_CONFIG_HEADERS

automake 1.13 errors if AM_CONFIG_HEADER is used in configure script.
ares_private.h: use again memdebug.h instead of curl_memdebug.h
configure: fix automake 1.13 compatibility

Tested with:

buildconf: autoconf version 2.69
buildconf: autom4te version 2.69
buildconf: autoheader version 2.69
buildconf: automake version 1.13.1
buildconf: aclocal version 1.13.1
buildconf: libtool version 2.4
buildconf: GNU m4 version 1.4.16
configure: autotools compatibility fixes - step I

Fix proper macro expansion order across autotools versions for
C compiler and preprocessor program checks.
zz40-xc-ovr.m4: provide XC_CONFIGURE_PREAMBLE macro
configure: use XC_CONFIGURE_PREAMBLE early checks

Some basic checks we make were placed early enough in generated
configure script when using autoconf 2.5X versions. Newer autoconf
versions expand these checks much further into the configure script,
rendering them useless. Using XC_CONFIGURE_PREAMBLE fixes placement
of early intended checks across all our autoconf supported versions.
zz40-xc-ovr.m4: redirect errors and warnings to stderr