x86, um: switch to generic fork/vfork/clone

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index 0761175..8f51c39 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -25,6 +25,7 @@
 	select HAVE_AOUT
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select MODULES_USE_ELF_REL
+	select CLONE_BACKWARDS
 
 config X86_64
 	def_bool 64BIT