Presumably these warnings will be fixed upstream at some point.
contrib/libxo/xo/xo.c:99:9: error: variable 'hflag' set but not used [-Werror,-Wunused-but-set-variable]
int hflag = 0, jflag = 0, tflag = 0, ^
contrib/libxo/xo/xo.c:99:20: error: variable 'jflag' set but not used [-Werror,-Wunused-but-set-variable]
int hflag = 0, jflag = 0, tflag = 0, ^
contrib/libxo/xo/xo.c:99:31: error: variable 'tflag' set but not used [-Werror,-Wunused-but-set-variable]
int hflag = 0, jflag = 0, tflag = 0, ^
contrib/libxo/xo/xo.c:100:2: error: variable 'zflag' set but not used [-Werror,-Wunused-but-set-variable]
zflag = 0, qflag = 0, star1 = 0, star2 = 0; ^
contrib/libxo/xo/xo.c:100:13: error: variable 'qflag' set but not used [-Werror,-Wunused-but-set-variable]
zflag = 0, qflag = 0, star1 = 0, star2 = 0; ^