stat-time, timespec, u64: support naive out-of-dir builds * lib/stat-time.c, lib/timespec.c, lib/u64.c: Use '#include "foo.h"', not '#include <foo.h>', when including one's own interface. This works better when configuring with out-of-directory builds, since packages need not add an otherwise-unnecessary -I$(topdir_src)/lib to DEFAULT_INCLUDES.

#include <config.h>
#define _GL_TIMESPEC_INLINE _GL_EXTERN_INLINE
#include "timespec.h"