selftests/x86: Add a fork() to entry_from_vm86 to catch fork bugs

selftests/x86: Add a fork() to entry_from_vm86 to catch fork bugs

Mere possession of vm86 state is strange.  Make sure that nothing
gets corrupted if we fork after calling vm86().

Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Stas Sergeev <[email protected]>
Link: http://lkml.kernel.org/r/08f83295460a80e41dc5e3e81ec40d6844d316f5.1446270067.git.luto@kernel.org
Signed-off-by: Thomas Gleixner <[email protected]>