Drop support for getting signal descriptions from sys_siglist[].

It appears that all platforms that have sys_siglist[] also have
strsignal(), making that fallback case in pg_strsignal() dead code.
Getting rid of it allows dropping a configure test, which seems worth
more than providing textual signal descriptions on whatever platforms
might still hypothetically have use for the fallback case.

Discussion: https://postgr.es/m/25758.1544983503@sss.pgh.pa.us

configure

@@ -16064,24 +16064,6 @@ esac
 
 fi
 
-ac_fn_c_check_decl "$LINENO" "sys_siglist" "ac_cv_have_decl_sys_siglist" "#include <signal.h>
-/* NetBSD declares sys_siglist in unistd.h.  */
-#ifdef HAVE_UNISTD_H
-# include <unistd.h>
-#endif
-
-"
-if test "x$ac_cv_have_decl_sys_siglist" = xyes; then :
-  ac_have_decl=1
-else
-  ac_have_decl=0
-fi
-
-cat >>confdefs.h <<_ACEOF
-#define HAVE_DECL_SYS_SIGLIST $ac_have_decl
-_ACEOF
-
-
 ac_fn_c_check_func "$LINENO" "syslog" "ac_cv_func_syslog"
 if test "x$ac_cv_func_syslog" = xyes; then :
   ac_fn_c_check_header_mongrel "$LINENO" "syslog.h" "ac_cv_header_syslog_h" "$ac_includes_default"

configure.in

@@ -1787,14 +1787,6 @@ if test "$PORTNAME" = "cygwin"; then
   AC_LIBOBJ(dirmod)
 fi
 
-AC_CHECK_DECLS([sys_siglist], [], [],
-[#include <signal.h>
-/* NetBSD declares sys_siglist in unistd.h.  */
-#ifdef HAVE_UNISTD_H
-# include <unistd.h>
-#endif
-])
-
 AC_CHECK_FUNC(syslog,
               [AC_CHECK_HEADER(syslog.h,
                                [AC_DEFINE(HAVE_SYSLOG, 1, [Define to 1 if you have the syslog interface.])])])

src/include/pg_config.h.in

@@ -192,10 +192,6 @@
    don't. */
 #undef HAVE_DECL_STRTOULL
 
-/* Define to 1 if you have the declaration of `sys_siglist', and to 0 if you
-   don't. */
-#undef HAVE_DECL_SYS_SIGLIST
-
 /* Define to 1 if you have the `dlopen' function. */
 #undef HAVE_DLOPEN
 

src/port/pgstrsignal.c

@@ -31,7 +31,7 @@
  * the string will remain valid across later calls to strsignal().
  *
  * This version guarantees to return a non-NULL pointer, although
- * some platforms' versions of strsignal() do not.
+ * some platforms' versions of strsignal() reputedly do not.
  */
 const char *
 pg_strsignal(int signum)
@@ -40,21 +40,18 @@ pg_strsignal(int signum)
 
 	/*
 	 * If we have strsignal(3), use that --- but check its result for NULL.
-	 * Otherwise, if we have sys_siglist[], use that; just out of paranoia,
-	 * check for NULL there too.  (We assume there is no point in trying both
-	 * APIs.)
 	 */
-#if defined(HAVE_STRSIGNAL)
+#ifdef HAVE_STRSIGNAL
 	result = strsignal(signum);
 	if (result)
 		return result;
-#elif defined(HAVE_DECL_SYS_SIGLIST) && HAVE_DECL_SYS_SIGLIST
+#else
-	if (signum > 0 && signum < NSIG)
+
-	{
+	/*
-		result = sys_siglist[signum];
+	 * We used to have code here to try to use sys_siglist[] if available.
-		if (result)
+	 * However, it seems that all platforms with sys_siglist[] have also had
-			return result;
+	 * strsignal() for many years now, so that was just a waste of code.
-	}
+	 */
 #endif
 
 	/*