https://github.com/libsdl-org/autoconf/commit/c7b8a371b47429291c9737ceff84d312014d41e3
From c7b8a371b47429291c9737ceff84d312014d41e3 Mon Sep 17 00:00:00 2001
From: Paul Eggert <[EMAIL REDACTED]>
Date: Fri, 7 Aug 2015 18:09:17 -0700
Subject: [PATCH] Add /opt/X11/include to X search path
* lib/autoconf/libs.m4 (_AC_PATH_X_DIRECT):
Add /opt/X11/include for OS X.
Problem reported by Daniel Macks at:
http://lists.gnu.org/archive/html/bug-autoconf/2015-08/msg00002.html
(cherry picked from commit 57ec362325a9b58d719c834d06653cfa7e2aa894)
---
lib/autoconf/libs.m4 | 2 ++
1 file changed, 2 insertions(+)
diff --git a/lib/autoconf/libs.m4 b/lib/autoconf/libs.m4
index 7a8f2b67..d419bb18 100644
--- a/lib/autoconf/libs.m4
+++ b/lib/autoconf/libs.m4
@@ -237,6 +237,8 @@ ac_x_header_dirs='
/usr/local/include/X11R5
/usr/local/include/X11R4
+/opt/X11/include
+
/usr/X386/include
/usr/x386/include
/usr/XFree86/include/X11