Hi again @bikas,
File "arduino/hardware/avr/platform.txt" is not the corresponding one for the Arduino DUE, it is the platform file for AVR platforms (Arduino UNO, etc.).
According to my experience the root directory for the Arduino DUE platform on Linux is "$HOME/.arduino15" (I´m using Arduino IDE 1.6.5), and in windows "C:\Users<your-user-name>\AppData\Roaming".
In fact, if you have a look to the error file you have included, in your computer the directory is "c:\users\bikash\appdata\roaming\arduino15\packages\arduino\hardware\sam\1.6.4 (or 1.6.3)". There, you should find the platform.txt corresponding tothe DUE.
The problem you have is that the -std=gnu++11 flag is missing:
Arduino: 1.6.5 (Windows 8.1), Board: "Arduino Due (Programming Port)"
In file included from c:\users\bikash\appdata\roaming\arduino15\packages\arduino\tools\arm-none-eabi-gcc\4.8.3-2014q1\arm-none-eabi\include\c++\4.8.3\cstdint:35:0,
from C:\Users\bikash\Documents\Arduino\libraries\soft_uart/soft_uart.h:40,
from soft_uart_serial_test.ino:39:
c:\users\bikash\appdata\roaming\arduino15\packages\arduino\tools\arm-none-eabi-gcc\4.8.3-2014q1\arm-none-eabi\include\c++\4.8.3\bits\c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
...
As I mentioned previously, just add that flag to the DUE's platform file:
compiler.cpp.flags=-c -g -Os -std=gnu++11 {compiler.warning_flags} -ffunction-sections -fdata-sections -nostdlib -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -Dprintf=iprintf -MMD
Best.