Test at compile time whether siginfo_t is usable for --remote (#119).

src/include/config.h.in

@@ -223,6 +223,9 @@
 /* Define to the version of this package. */
 #undef PACKAGE_VERSION
 
+/* Signal handlers can determine the sending PID */
+#undef SIGINFO_PROVIDES_PID
+
 /* Define to 1 if all of the C90 standard headers exist (not just the ones
    required in a freestanding environment). This macro is provided for
    backward compatibility; new code need not use it. */

src/include/pv-internal.h

@@ -154,13 +154,13 @@ struct pvstate_s {
 		struct sigaction old_sigint;
 		struct sigaction old_sighup;
 		struct sigaction old_sigterm;
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 		struct sigaction old_sigusr2;
 #endif
 		struct sigaction old_sigalrm;
 		struct timespec tstp_time;	 /* see pv_sig_tstp() / __cont() */
 		struct timespec toffset;	 /* total time spent stopped */
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 		volatile sig_atomic_t rxusr2;	 /* whether SIGUSR2 was received */
 		volatile pid_t sender;		 /* PID of sending process for SIGUSR2 */
 #endif

src/include/pv.h

@@ -237,7 +237,7 @@ extern off_t pv_calc_total_size(pvstate_t);
  */
 extern void pv_sig_init(pvstate_t);
 
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 /*
  * Return true if SIGUSR2 has been received, and indicate the sender.
  */