most of set_current_blocked() callers want SIGKILL/SIGSTOP removed from set

Only 3 out of 63 do not.  Renamed the current variant to __set_current_blocked(),
added set_current_blocked() that will exclude unblockable signals, switched
open-coded instances to it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/um/kernel/signal.c

@@ -15,10 +15,6 @@
 EXPORT_SYMBOL(block_signals);
 EXPORT_SYMBOL(unblock_signals);
 
-#define _S(nr) (1<<((nr)-1))
-
-#define _BLOCKABLE (~(_S(SIGKILL) | _S(SIGSTOP)))
-
 /*
  * OK, we're invoking a handler
  */