Has anyone had this and recognises the cause now? Here is what is output
/tmp/build1805287591596065479.tmp/WiFiWebServer.cpp.o
/opt/arduino-1.6.3/hardware/esp8266com/esp8266/tools/linux/xtensa-lx106-elf/bin/xtensa-lx106-elf-g++: /opt/arduino-1.6.3/hardware/esp8266com/esp8266/tools/linux/xtensa-lx106-elf/bin/xtensa-lx106-elf-g++: cannot execute binary file
/opt/arduino-1.6.3/hardware/esp8266com/esp8266/tools/linux/xtensa-lx106-elf/bin/xtensa-lx106-elf-g++ returned 126
Error compiling.