Python extension fails to build on Debian sid

[pepone]

-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 -Wdate-time
-D_FORTIFY_SOURCE=2 -c ../cpp/src/Slice/Grammar.cpp -o modules/IcePy/build/arm-
linux-gnueabihf/shared/pic/Grammar.o
cc1plus: error: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is
not valid for C++ [-Werror]
cc1plus: error: ‘-Werror=’ argument

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1067911