guile build problem with gcc 4.6.0

[Douglas Mencken]

GC 4.6.0 introduced new warning: unused-but-set-variable, so with
-Werror it's now impossible to build guile.

/bin/bash ../libtool  --tag=CC   --mode=compile
powerpc-gnu-linux-uclibc-gcc -DHAVE_CONFIG_H   -I.. -I.. -I..
-pthread -g -O2 -Wall -Wmissing-prototypes -Werror -MT
libguile_la-async.lo -MD -MP -MF .deps/libguile_la-async.Tpo -c -o
libguile_la-async.lo `test -f 'async.c' || echo './'`async.c
libtool: compile:  powerpc-gnu-linux-uclibc-gcc -DHAVE_CONFIG_H -I..
-I.. -I.. -pthread -g -O2 -Wall -Wmissing-prototypes -Werror -MT
libguile_la-async.lo -MD -MP -MF .deps/libguile_la-async.Tpo -c
async.c  -fPIC -DPIC -o .libs/libguile_la-async.o
async.c: In function 'scm_i_queue_async_cell':
async.c:243:14: error: variable 'count' set but not used
[-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors

make[3]: *** [libguile_la-async.lo] Error 1