From d6e315d25db5c2a10b552cddd3aec93ce9398f26 Mon Sep 17 00:00:00 2001
From: David Adam <zanchey@ucc.gu.uwa.edu.au>
Date: Thu, 20 Dec 2018 21:36:01 +0800
Subject: [PATCH] cmake: define _GNU_SOURCE

Fixes the build on Cygwin. Analogous to AC_USE_SYSTEM_EXTENSIONS under Autoconf.

Closes #5423.
---
 config_cmake.h.in | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/config_cmake.h.in b/config_cmake.h.in
index 2c23ad452..d234acba9 100644
--- a/config_cmake.h.in
+++ b/config_cmake.h.in
@@ -142,6 +142,11 @@
 /* Define to 1 if tparm accepts a fixed amount of paramters. */
 #cmakedefine TPARM_SOLARIS_KLUDGE 1
 
+/* Enable GNU extensions on systems that have them.  */
+#ifndef _GNU_SOURCE
+# define _GNU_SOURCE 1
+#endif
+
 /* The size of wchar_t in bits. */
 #define WCHAR_T_BITS ${WCHAR_T_BITS}