Hi André,
we are seeing a build error on your machine when locales in uClibc-ng are enabled: http://autobuild.buildroot.net/results/d5b/d5ba81eea9223569ba5b363551c4a2f70...
Can you show us locale -a from your machine?
For a working tolower(), the uClibc-ng code needs to use setlocale on the host.
But it seems only these are tried to use: en_US en_US en_GB
best regards Waldemar