mgetgroups: port to strict OS X

* doc/glibc-functions/getgrouplist.texi (getgrouplist):
Document the getgrouplist problem.
* lib/mgetgroups.c (getgrouplist_gids) [HAVE_GETGROUPLIST]:
New macro.
(mgetgroups): Use it.
* m4/mgetgroups.m4 (gl_MGETGROUPS):
Check for OS X signature for getgrouplist.

doc/glibc-functions/getgrouplist.texi

@@ -10,6 +10,10 @@ Portability problems fixed by Gnulib:
 
 Portability problems not fixed by Gnulib:
 @itemize
+@item
+This function takes @code{int} instead of @code{gid_t} parameters
+on some platforms: OS X 10.11.
+
 @item
 This function is missing on some platforms:
 Minix 3.1.8, AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 11 2011-11, Cygwin 1.7.9, mingw, MSVC 9, BeOS.

lib/mgetgroups.c

@@ -64,6 +64,11 @@ mgetgroups (char const *username, gid_t gid, gid_t **groups)
   gid_t *g;
 
 #if HAVE_GETGROUPLIST
+# if HAVE_GETGROUPLIST_WITH_INT
+#  define getgrouplist_gids(g) ((int *) (g))
+# else
+#  define getgrouplist_gids(g) (g)
+# endif
   /* We prefer to use getgrouplist if available, because it has better
      performance characteristics.
 
@@ -87,7 +92,8 @@ mgetgroups (char const *username, gid_t gid, gid_t **groups)
           int last_n_groups = max_n_groups;
 
           /* getgrouplist updates max_n_groups to num required.  */
-          ng = getgrouplist (username, gid, g, &max_n_groups);
+          ng = getgrouplist (username, gid, getgrouplist_gids (g),
+                             &max_n_groups);
 
           /* Some systems (like Darwin) have a bug where they
              never increase max_n_groups.  */

m4/mgetgroups.m4

@@ -1,4 +1,4 @@
-#serial 5
+#serial 6
 dnl Copyright (C) 2007-2015 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,5 +6,41 @@ dnl with or without modifications, as long as this notice is preserved.
 
 AC_DEFUN([gl_MGETGROUPS],
 [
+  AC_CHECK_HEADERS_ONCE([grp.h])
   AC_CHECK_FUNCS_ONCE([getgrouplist])
+  if test "$ac_cv_func_getgrouplist" = yes; then
+    AC_CACHE_CHECK([for getgrouplist with int signature],
+      [gl_cv_getgrouplist_with_int],
+      [gl_cv_getgrouplist_with_int=no
+       AC_COMPILE_IFELSE(
+         [AC_LANG_PROGRAM(
+            [[#if HAVE_GRP_H
+               #include <grp.h>
+              #endif
+              int groups[1];
+              int ngroups = 1;
+              int getgrouplist (char const *, gid_t, gid_t *, int *);
+            ]],
+            [[
+              return - getgrouplist ("root", 0, groups, &ngroups);
+            ]])],
+         [],
+         [AC_COMPILE_IFELSE(
+           [AC_LANG_PROGRAM(
+              [[#if HAVE_GRP_H
+                 #include <grp.h>
+                #endif
+                int groups[sizeof (gid_t) == sizeof (int) ? 1 : -1];
+                int ngroups = 1;
+                int getgrouplist (char const *, int, int *, int *);
+              ]],
+              [[
+                return - getgrouplist ("root", 0, groups, &ngroups);
+              ]])],
+            [gl_cv_getgrouplist_with_int=yes])])])
+    if test "$gl_cv_getgrouplist_with_int" = yes; then
+      AC_DEFINE([HAVE_GETGROUPLIST_WITH_INT], 1,
+        [Define to 1 if getgrouplist accepts and returns int and not gid_t.])
+    fi
+  fi
 ])