+dnl Look for the initgroups() declaration. On AIX 4.[13], Solaris 4.1.3, and
+dnl ULTRIX 4.2A the function is defined in libc but there's no declaration in
+dnl any system header.
+dnl
+dnl On Solaris 2.[456], the declaration is in <grp.h>. On HP-UX 9-11 and
+dnl (reportedly) FreeBSD 3.[23], it's in <unistd.h>. Any other locations we
+dnl need to check?
+AC_EGREP_HEADER(initgroups, grp.h, AC_DEFINE(INITGROUPS_HEADER, <grp.h>),
+ AC_EGREP_HEADER(initgroups, unistd.h,
+ AC_DEFINE(INITGROUPS_HEADER, <unistd.h>)))
+