Added checking for QNX operating system to make mbedtls build on QNX
diff --git a/library/timing.c b/library/timing.c
index a7c7ff0..56f29bd 100644
--- a/library/timing.c
+++ b/library/timing.c
@@ -39,7 +39,7 @@
 #if !defined(MBEDTLS_TIMING_ALT)
 
 #if !defined(unix) && !defined(__unix__) && !defined(__unix) && \
-    !defined(__APPLE__) && !defined(_WIN32)
+    !defined(__APPLE__) && !defined(_WIN32) && !defined(__QNXNTO__)
 #error "This module only works on Unix and Windows, see MBEDTLS_TIMING_C in config.h"
 #endif