tools/virtio: fix up compiler.h stub

Add #undef __user before and after including compiler_types.h to avoid
redefinition warnings when compiling with system headers that also
define __user. This allows tools/virtio to build without warnings.

Additionally, stub out __must_check

Created using Cursor CLI.

Message-ID: <[e-mail]>
Acked-by: Jason Wang <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>

tools/virtio/linux/compiler.h

···
 #ifndef LINUX_COMPILER_H
 #define LINUX_COMPILER_H
 
+/* Avoid redefinition warnings */
+#undef __user
 #include "../../../include/linux/compiler_types.h"
+#undef __user
+#define __user
 
 #define WRITE_ONCE(var, val) \
 	(*((volatile typeof(val) *)(&(var))) = (val))
···
 	auto __v = (expr);						\
 	__v;								\
 })
+
+#define __must_check
 
 #endif