um: merge os-Linux/tls.c into arch/x86/um/os-Linux/tls.c

it's i386-specific; moreover, analogs on other targets have
incompatible interface - PTRACE_GET_THREAD_AREA does exist
elsewhere, but struct user_desc does *not*

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

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

@@ -29,6 +29,9 @@ typedef struct user_desc user_desc_t;
 
 # endif /* __KERNEL__ */
 
+extern int os_set_thread_area(user_desc_t *info, int pid);
+extern int os_get_thread_area(user_desc_t *info, int pid);
+
 #ifdef __i386__
 #define GDT_ENTRY_TLS_MIN_I386 6
 #define GDT_ENTRY_TLS_MIN_X86_64 12