simple signal handler and kill(2) support.

arch/x86/kernel/include/signal.h

@@ -0,0 +1,18 @@
+#define _NSIG		64
+#define _NSIG_BPW	64
+#define _NSIG_WORDS (_NSIG / _NSIG_BPW)
+
+typedef struct {
+        unsigned long sig[_NSIG_WORDS];
+} sigset_t;
+
+struct sigaction {
+	void (*sa_handler)(int);
+	unsigned long sa_flags;
+	void (*sa_restorer)(int);
+	sigset_t sa_mask;
+};
+
+struct k_sigaction {
+        struct sigaction sa;
+};