package/apitrace: needs wchar

package/apitrace: needs wchar

apitrace uses its own version of gtest which depends on wchar since
version 8.0 and
https://github.com/apitrace/apitrace/commit/85cf7c8b86129699246574dfeec846e88a3f88a2

Moreover, apitrace also uses wcslen in trace_writer.cpp since at least
version 8.0 and
https://github.com/apitrace/apitrace/commit/5e9a2b11b248aaa2f6f353bbcf9f600d65bcaf51

Fixes:
 - http://autobuild.buildroot.org/results/5f27556ccc9daec578fe1bf2ed516ca9921ed474

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>