c:\programme\arduino-1.5.2\hardware\tools\g++_arm_none_eabi\bin../lib/gcc/arm-none-eabi/4.4.1/../../../../arm-none-eabi/include/sys/reent.h:490: error: #if with no expression
The Error is outside of your sketch. Head honcho g++ tells you that the file reent.h which is to be used for compiling code for the SAM3X is botched. So the message ensues. Have you messed in this file before?
This file is not used for the Atmega Mega so no error occur.
Hope this helps,
Transistorfips