Add changelog for posix definition
Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/ChangeLog.d/posix-define.txt b/ChangeLog.d/posix-define.txt
new file mode 100644
index 0000000..98cf2d0
--- /dev/null
+++ b/ChangeLog.d/posix-define.txt
@@ -0,0 +1,6 @@
+Bugfix
+ * In library/net_sockets.c, _POSIX_C_SOURCE and _XOPEN_SOURCE are
+ defined to specific values. If the code is used in a context
+ where these are already defined, this can result in a compilation
+ error. Instead, assume that if they are defined, the values will
+ be adequate to build Mbed TLS.