Add POSIX type sig_atomic_t

include/signal.h

@@ -194,6 +194,12 @@
 typedef uint32_t sigset_t;   /* Bit set of 32 signals */
 #define __SIGSET_T_DEFINED 1
 
+/* Possibly volatile-qualified integer type of an object that can be accessed
+ * as an atomic entity, even in the presence of asynchronous interrupts.
+ */
+
+typedef volatile int sig_atomic_t;
+
 /* This defines the type of the siginfo si_value field */
 
 union sigval