This warning fires here:
/home/travis/build/jaagr/polybar/src/utils/command.cpp:135:46: error: equality comparison with extraneous parentheses [-Werror,-Wparentheses-equality]
} else if ((((*(int *) &(m_forkstatus))) == 0xffff)) {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
and as this system macro cannot be changed, let's not turn this into an error