_g_callable_info_invoke accounts for the arg direction when determining the ffi type to use (using ffi_type_pointer for inout and out args), but g_callable_info_get_ffi_arg_types doesn't.

This causes problems on at least x86-64 because ffi uses SSE registers for floats and general purpose registers for pointers, so when passing a float inout arg, the caller (using _g_callable_info_invoke) passes it in a general purpose register, but the closure (created with g_callable_info_prepare_closure, which calls g_callable_info_get_ffi_arg_types) expects it in an SSE register.  As a result it dereferences a random pointer and crashes.