package/azure-iot-sdk-c: needs wchar

package/azure-iot-sdk-c: needs wchar

wchar is needed since version LTS_07_2020_Ref01 which bumped internal
umock with
https://github.com/Azure/azure-iot-sdk-c/commit/8a27860452ec7345bce84d6690b0e8d167b7560a

Indeed umock unconditionally depends on wchar since
https://github.com/Azure/umock-c/commit/6b8e0160defb23ec4fde159ba6389cf61e352a0b

Fixes:
 - http://autobuild.buildroot.org/results/ad7ecd00d8f55c7cae5886c38c097ff0d071a962

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>