Fix compilation using md5 in Sloeber

This issue: Sloeber/arduino-eclipse-plugin#1028 has a known fix: Sloeber/arduino-eclipse-plugin#1028 (comment) 

This commit will add the patch to the existing sources.

Author: madhephaestus

tools/sdk/include/mbedtls/mbedtls/md5.h

@@ -31,7 +31,9 @@
 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "config.h"
 #else
-#include MBEDTLS_CONFIG_FILE
+#define VAL(str) #str
+#define TOSTRING(str) VAL(str)
+#include TOSTRING(MBEDTLS_CONFIG_FILE) 
 #endif
 
 #include <stddef.h>