Merge: tests/base_autocast: workaround a gcc bug

Versions of gcc between bellow 6.4.1 and 7.3.1 failed to compile
correctly the generated C.
So this changes the Nit, so the C can be compiled with buggy gcc versions.

Cf https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85244 for details

Pull-Request: #2733