getloadavg: don't depend on c-strtod, cloexec, fcntl-safer

getloadavg: don't depend on c-strtod, cloexec, fcntl-safer

See the thread rooted at
<http://lists.gnu.org/archive/html/bug-gnulib/2011-02/msg00090.html>.
* lib/getloadavg.c: Do not include c-strtod.h, cloexec.h, or fcntl--.h.
Include <fcntl.h> only if (defined __linux__ || defined __CYGWIN__
|| defined SUNOS_5 || (defined LOAD_AVE_TYPE && !  defined
__VMS)); previously it was always included (via fcntl--.h).
(getloadavg): Do not use c_strtod.  Instead, approximate it by
hand; this is good enough for load averages.  Also, do not use
set_cloexec_flag; instead, use the O_CLOEXEC and F_DUPFD_CLOEXEC
flags directly if available and don't bother otherwise.  (Packages
that need the extra reliability should use the modules that define
these flags on older platforms that lack them.)
* modules/getloadavg (Depends-on): Remove c-strtod, cloexec,
fcntl-safer.