patch 9.0.1450: MacOS: building fails if clock_gettime() is not available

Problem:    MacOS: building fails if clock_gettime() is not available.
Solution:   Add a configure check for clock_gettime(). (closes #12242)
diff --git a/src/auto/configure b/src/auto/configure
index 77d2f5e..28eb7f3 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -12528,7 +12528,8 @@
 	getpgid setpgid setsid sigaltstack sigstack sigset sigsetjmp sigaction \
 	sigprocmask sigvec strcasecmp strcoll strerror strftime stricmp strncasecmp \
 	strnicmp strpbrk strptime strtol tgetent towlower towupper iswupper \
-	tzset usleep utime utimes mblen ftruncate unsetenv posix_openpt
+	tzset usleep utime utimes mblen ftruncate unsetenv posix_openpt \
+	clock_gettime
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"