buildroot

putty: needs wchar support

putty uses mbstate_t, which is a wchar related definition, so wchar
support is needed in the toolchain.

Fixes:

  http://autobuild.buildroot.net/results/0e3f4306513b79306d43338eced890205632c395/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>