In SoftwareSerial.h, change this line:
void write(uint8_t);
To :
size_t write(uint8_t);
And in SoftwareSerial.cpp, change this:
size_t SoftwareSerial::write(uint8_t )
{
if (_baudRate == 0)
return;
...
...
To:
size_t SoftwareSerial::write(uint8_t )
{
if (_baudRate == 0)
return 0;
...
...