stat: port birthtime to Solaris 11

stat: port birthtime to Solaris 11

Problem reported by Rich Burridge.
* src/stat.c [HAVE_GETATTRAT]: Include <attr.h>, <sys/nvpair.h>.
(print_statfs, print_stat, print_it):
Pass fd, too, for the benefit of get_birthtime.
All uses changed.
(get_birthtime): New function, for porting to Solaris 11.
(print_stat): Use it.

* configure.ac (getattrat, LIB_NVPAIR): New checks.
* src/local.mk (src_stat_LDADD): Add $(LIB_NVPAIR).