glibc has problems with proper static compilation of some functions.

You hit this when you see warnings like

aux.o: In function `parsegid':
aux.c:(.text+0x5ff): warning: Using 'getgrgid' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking

You can get around this by bringing over libpwdgrp from Busybox
(http://busybox.net).

Fetch busybox and compile it with "CONFIG_USE_BB_PWD_GRP=yes" (settable via

Login/Password Management Utilities / Use internal password and group functions rather than system functions

in menuconfig). Then copy libpwdgrp/libpwdgrp.a here, and use the
USE_BB_LIBPWDGRP=1 setting when compiling reclinker.

If you wonder about the background of this phenomenon, read the associated help
text in menuconfig.