KVM: selftests: Call a dummy helper in VM/vCPU ioctls() to enforce type

Replace the goofy static_assert on the size of the @vm/@vcpu parameters
with a call to a dummy helper, i.e. let the compiler naturally complain
about an incompatible type instead of homebrewing a poor replacement.
Reported-by: Andrew Jones <drjones@redhat.com>
Fixes: fcba483e ("KVM: selftests: Sanity check input to ioctls() at build time")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220613161942.1586791-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -200,9 +200,11 @@ static inline bool kvm_has_cap(long cap)
 #define kvm_ioctl(kvm_fd, cmd, arg) \
 	_kvm_ioctl(kvm_fd, cmd, #cmd, arg)
 
+static __always_inline void static_assert_is_vm(struct kvm_vm *vm) { }
+
 #define __vm_ioctl(vm, cmd, arg)				\
 ({								\
-	static_assert(sizeof(*(vm)) == sizeof(struct kvm_vm), "");		\
+	static_assert_is_vm(vm);				\
 	kvm_do_ioctl((vm)->fd, cmd, arg);			\
 })
 
@@ -216,9 +218,12 @@ static inline bool kvm_has_cap(long cap)
 #define vm_ioctl(vm, cmd, arg)					\
 	_vm_ioctl(vm, cmd, #cmd, arg)
 
+
+static __always_inline void static_assert_is_vcpu(struct kvm_vcpu *vcpu) { }
+
 #define __vcpu_ioctl(vcpu, cmd, arg)				\
 ({								\
-	static_assert(sizeof(*(vcpu)) == sizeof(struct kvm_vcpu), "");		\
+	static_assert_is_vcpu(vcpu);				\
 	kvm_do_ioctl((vcpu)->fd, cmd, arg);			\
 })