Fixed compiler error in auth_pam plugin

Code copied from 10.6

plugin/auth_pam/CMakeLists.txt

+IF(WIN32)
+  RETURN()
+ENDIF()
+
 INCLUDE (CheckIncludeFiles)
 INCLUDE (CheckFunctionExists)
 
@@ -15,8 +19,8 @@ CHECK_C_SOURCE_COMPILES(
 #include <grp.h>
 #include <unistd.h>
 int main() {
-  char *arg_1;
-  gid_t arg_2, arg_3;
+  char *arg_1= 0;
+  gid_t arg_2=0, arg_3;
   int arg_4;
   (void)getgrouplist(arg_1,arg_2,&arg_3,&arg_4);
   return 0;