um: Stop abusing __KERNEL__

Currently UML is abusing __KERNEL__ to distinguish between
kernel and host code (os-Linux). It is better to use a custom
define such that existing users of __KERNEL__ don't get confused.

Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/shared/sysdep/tls.h

@@ -1,7 +1,7 @@
 #ifndef _SYSDEP_TLS_H
 #define _SYSDEP_TLS_H
 
-# ifndef __KERNEL__
+#ifdef __UM_HOST__
 
 /* Change name to avoid conflicts with the original one from <asm/ldt.h>, which
  * may be named user_desc (but in 2.4 and in header matching its API was named
@@ -22,11 +22,11 @@ typedef struct um_dup_user_desc {
 #endif
 } user_desc_t;
 
-# else /* __KERNEL__ */
+#else /* __UM_HOST__ */
 
 typedef struct user_desc user_desc_t;
 
-# endif /* __KERNEL__ */
+#endif /* __UM_HOST__ */
 
 extern int os_set_thread_area(user_desc_t *info, int pid);
 extern int os_get_thread_area(user_desc_t *info, int pid);