gnutls: make crywrap a tools option

crywrap now needs wchar support so just build it when tools are enabled.
It's also a tool so it belongs there anyway.
Fixes:
http://autobuild.buildroot.net/results/418/418ce71eecc1db725e3b3f092131a01cb1666a60/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>