I solved this problem. It seems that libical does not support the ./configure method anymore. You should use cmake(an up2date version, 2.8.2 didn't worked for me) instead.
For me, the build process now looks like this:
$ export CC=arm-merlin-linux-uclibc-gcc
$ export CXX=arm-merlin-linux-uclibc-g++
$ mkdir build && cd build
$ cmake -DCMAKE_INSTALL_PREFIX=/opt/cross/libical ..
...
$ make
...
$ make install
I hope this helps someone.