uml: track and make up lost ticks

Alarm delivery could be noticably late in the !CONFIG_NOHZ case because lost
ticks weren't being taken into account.  This is now treated more carefully,
with the time between ticks being calculated and the appropriate number of
ticks delivered to the timekeeping system.

Cc: Nix <nix@esperi.org.uk>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 3f1694b..5aade60 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -12,6 +12,7 @@
 #include "as-layout.h"
 #include "kern_util.h"
 #include "os.h"
+#include "process.h"
 #include "sysdep/barrier.h"
 #include "sysdep/sigcontext.h"
 #include "user.h"