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/config.h.in b/src/config.h.in
index b114480..5d01e2c 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -496,3 +496,6 @@
 
 /* Define to inline symbol or empty */
 #undef inline
+
+/* Define if _SC_SIGSTKSZ is available via sysconf() */
+#undef HAVE_SYSCONF_SIGSTKSZ