ok, new bug for me: I have autoconf (GNU Autoconf) 2.52 and I've also
downloaded libtool from GNU version 1.4.2. This is the error I get:

Making all in tests
make[5]: Entering directory `/tmp/gstreamer/libs/ext/cothreads/tests'
source='pth.c' object='pth-pth.o' libtool=no \
depfile='.deps/pth-pth.Po' tmpdepfile='.deps/pth-pth.TPo' \
depmode=gcc /bin/sh ../depcomp \
gcc -DHAVE_CONFIG_H -I. -I. -I../cothreads    -I/usr/include/glib-2.0
-I/usr/lib/glib-2.0/include   -I.. -g -O2 -c -o pth-pth.o `test -f pth.c ||
echo './'`pth.c
/bin/sh ../libtool --mode=link gcc  -g -O2   -o pth  pth-pth.o
../cothreads/libcothreads.la 
mkdir .libs
gcc -g -O2 -o pth pth-pth.o  ../cothreads/.libs/libcothreads.al
source='cothreads.c' object='cothreads-cothreads.o' libtool=no \
depfile='.deps/cothreads-cothreads.Po'
tmpdepfile='.deps/cothreads-cothreads.TPo' \
depmode=gcc /bin/sh ../depcomp \
gcc -DHAVE_CONFIG_H -I. -I. -I../cothreads    -I/usr/include/glib-2.0
-I/usr/lib/glib-2.0/include   -I.. -g -O2 -c -o cothreads-cothreads.o `test
-f cothreads.c || echo './'`cothreads.c
/bin/sh ../libtool --mode=link gcc  -g -O2   -o cothreads 
cothreads-cothreads.o ../cothreads/libcothreads.la 
gcc -g -O2 -o cothreads cothreads-cothreads.o 
../cothreads/.libs/libcothreads.al
../cothreads/.libs/libcothreads.al(libcothreads_la-cothreads.lo): In
function `cothreads_init':
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:111: undefined
reference to `g_log'
../cothreads/.libs/libcothreads.al(libcothreads_la-cothreads.lo): In
function `cothreads_init_thread':
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:186: undefined
reference to `g_log'
../cothreads/.libs/libcothreads.al(libcothreads_la-cothreads.lo): In
function `cothread_create':
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:262: undefined
reference to `g_log'
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:267: undefined
reference to `g_log'
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:276: undefined
reference to `g_log'
../cothreads/.libs/libcothreads.al(libcothreads_la-cothreads.lo):/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:375:
more undefined references to `g_log' follow
../cothreads/.libs/libcothreads.al(libcothreads_la-cothreads.lo): In
function `cothread_chunk_new':
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:543: undefined
reference to `g_malloc0'
/tmp/gstreamer/libs/ext/cothreads/cothreads/cothreads.c:545: undefined
reference to `g_malloc0'
collect2: ld returned 1 exit status
make[5]: *** [cothreads] Error 1
make[5]: Leaving directory `/tmp/gstreamer/libs/ext/cothreads/tests'
make[4]: *** [all-recursive] Error 1
make[4]: Leaving directory `/tmp/gstreamer/libs/ext/cothreads'
make[3]: *** [all-recursive] Error 1
make[3]: Leaving directory `/tmp/gstreamer/libs/ext'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/tmp/gstreamer/libs'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/tmp/gstreamer'
make: *** [all] Error 2