emulators/virtualbox-ose-kmod: fix cross building

For cross building the CC variable is passed quoted with the target

the which configure script from VirtualBox expects it to only be the
name of the command and using which to determine if usable.

Replacing in the which_wrapper function the call of $* with only the
first argument, makes it accept cross building.

Cross building support is important for kmods as they are all cross
built to populate the kmods repositories

(cherry picked from commit 8b659812a21508795778a345dbbf7d08b7fcbb38)