patch 8.2.2550: signal stack size is wrong with latest glibc 2.34

Problem:    Signal stack size is wrong with latest glibc 2.34.
Solution:   Use sysconf(_SC_SIGSTKSZ) if available. (Zdenek Dohnal, closes
            #7895)
diff --git a/src/configure.ac b/src/configure.ac
index 58bfa19..798e9b8 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -4105,6 +4105,15 @@
 	AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SYSCONF),
 	AC_MSG_RESULT(not usable))
 
+dnl check if we have _SC_SIGSTKSZ via sysconf()
+AC_MSG_CHECKING(for _SC_SIGSTKSZ via sysconf())
+AC_TRY_COMPILE(
+[#include <unistd.h>],
+[	(void)sysconf(_SC_SIGSTKSZ);
+	],
+	AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SYSCONF_SIGSTKSZ),
+	AC_MSG_RESULT(not usable))
+
 AC_CHECK_SIZEOF([int])
 AC_CHECK_SIZEOF([long])
 AC_CHECK_SIZEOF([time_t])