Make zero-sized new standards-compliant

This fixes part of arduino#287.

Author: matthijskooijman

Diff for: cores/arduino/new.cpp

@@ -19,6 +19,10 @@
 #include "new.h"
 
 void * operator new(size_t size) {
+  // Even zero-sized allocations should return a unique pointer, but
+  // malloc does not guarantee this
+  if (size == 0)
+    size = 1;
   return malloc(size);
 }
 void * operator new[](size_t size) {