lang/mono6.8: fix build with llvm 16

exceptions-ppc.c:817:32: error: incompatible pointer to integer conversion assigning to 'host_mgreg_t' (aka 'long') from 'gpointer' (aka 'void *') [-Wint-conversion]

ctx->regs [PPC_FIRST_ARG_REG] = user_data;
                              ^ ~~~~~~~~~

exceptions-ppc.c:819:23: error: incompatible pointer to integer conversion assigning to 'unsigned long' from 'gpointer' (aka 'void *') [-Wint-conversion]

*(unsigned long *)sp = MONO_CONTEXT_GET_SP(ctx);
                     ^ ~~~~~~~~~~~~~~~~~~~~~~~~

exceptions-ppc.c:821:45: error: incompatible integer to pointer conversion passing 'unsigned long' to parameter of type 'gpointer' (aka 'void *') [-Wint-conversion]

mono_arch_setup_resume_sighandler_ctx(ctx, (unsigned long) async_cb);
                                           ^~~~~~~~~~~~~~~~~~~~~~~~

./mini.h:2384:77: note: passing argument to parameter 'func' here
void mono_arch_setup_resume_sighandler_ctx (MonoContext *ctx, gpointer func);

^

3 errors generated.