* modules/gethrxtime: New file.

* modules/gethrxtime: New file.
* modules/xnanosleep (Files): Add m4/xnanosleep.m4.
(Depends-on): Add gethrxtime.
(configure.ac): Add gl_XNANOSLEEP.
(Makefile.am): Remove lib_SOURCES line.

* lib/gethrxtime.h, lib/gethrxtime.c, lib/xtime.h: New files.
* lib/timespec.h (gettime): Return void, since it always
succeeds now.  All uses changed.
* lib/gettime.c (gettime) Likewise.
[HAVE_NANOTIME]: Prefer nanotime.
Assume gettimeofday succeeds, as POSIX requires.
Assime time () succeeds, since other code already does.
* lib/xnanosleep.c: Include xtime.h and gethrxtime.h, not xalloc.h.
(timespec_subtract): Remove.
(NANOSLEEP_BUG_WORKAROUND): New constant.
(xnanosleep): Use gethrxtime rather than gettime; this simplifies
things considerably.  Use it only on GNU/Linux hosts, since the
workaround shouldn't be needed elsewhere.

* m4/gethrxtime.m4, m4/xnanosleep.m4: New files.
* m4/gettime.m4 (gl_GETTIME): Check for nanotime.