Platform: Replace non throwing versions of new operator.

This change prevents inclusion of non throwing versions of the new operator from
the compiler standard library. On GCC, the non throwing version bring with it
some portion of the exception support code.

platform/mbed_retarget.cpp

@@ -1008,6 +1008,16 @@ void *operator new[](std::size_t count)
     return buffer;
 }
 
+void *operator new(std::size_t count, const std::nothrow_t& tag)
+{
+    return malloc(count);
+}
+
+void *operator new[](std::size_t count, const std::nothrow_t& tag)
+{
+    return malloc(count);
+}
+
 void operator delete(void *ptr)
 {
     if (ptr != NULL) {