[compiler-rt] Fix the prototype of ioctl interceptor

The interceptor of ioctl is using a non-standard prototype:

  INTERCEPTOR(int, ioctl, int d, unsigned request, void *arg)

At least on OS X, the request argument should be unsigned long and not 
just unsigned, and also instead of the last argument (arg), the function
should be accepting a variable number of arguments, so the prototype
should be:

  int ioctl(int fildes, unsigned long request, ...);

We can still keep using `unsigned` internally to save space, because we
know that all possible values of `request` will fit into it.

Reviewed at http://reviews.llvm.org/D7038

llvm-svn: 226926