Sorry, the patch was incomplete. configure needs to be changed as well
(it's difficult to regenerate it; autoconf itself was not C99-compatible
at the time, and later versions might produce a non-equivalent script.)
Thanks,
Florian
diff -ur vorbisgain-0.36.orig/configure vorbisgain-0.36/configure
--- vorbisgain-0.36.orig/configure 2005-02-06 18:41:37.000000000 +0100
+++ vorbisgain-0.36/configure 2019-09-09 15:58:47.721500962 +0200
@@ -3894,6 +3894,7 @@
cat >>conftest.$ac_ext <<_ACEOF
/* end confdefs.h. */
#include <ctype.h>
+#include <stdlib.h>
#if ((' ' & 0x0FF) == 0x020)
# define ISLOWER(c) ('a' <= (c) && (c) <= 'z')
# define TOUPPER(c) (ISLOWER(c) ? 'A' + ((c) - 'a') : (c))
diff -ur vorbisgain-0.36.orig/misc.c vorbisgain-0.36/misc.c
--- vorbisgain-0.36.orig/misc.c 2019-09-09 12:19:42.805189786 +0200
+++ vorbisgain-0.36/misc.c 2019-09-09 12:59:20.848918603 +0200
@@ -23,6 +23,7 @@
#else /* WIN32 */
#include <errno.h>
#include <ctype.h>
+#include <unistd.h>
#ifndef DISABLE_WINSIZE
