[PATCH v10] y2038: Provide conversion helpers for struct __timespec64

[Joseph Myers]

This has broken the build of glibc for i686-gnu as struct timeval isn't 
defined at this point in the build.

In file included from /scratch/jmyers/glibc-bot/install/compilers/i686-gnu/sysroot/include/hurd/hurd_types.h:24,
                 from ../hurd/hurd.h:30,
                 from ../sysdeps/hurd/include/hurd.h:2,
                 from hurdid.c:18:
../include/time.h:183:51: error: parameter 1 ('tv') has incomplete type
 valid_timeval_to_timespec64 (const struct timeval tv)
                              ~~~~~~~~~~~~~~~~~~~~~^~
../include/time.h:221:1: error: return type is an incomplete type
 valid_timespec64_to_timeval (const struct __timespec64 ts64)
 ^~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/time.h: In function 'valid_timespec64_to_timeval':
../include/time.h:223:18: error: storage size of 'tv' isn't known
   struct timeval tv;
                  ^~

-- 
Joseph S. Myers
joseph@codesourcery.com