Argument unused caused failure - Rebuild of the Debian archive with clang

"Argument unused caused failure" build failure(s) — clang 6.0

Unknown or unused arguments triggers errors with -Werror:
clang -Werror -ggdb3 foo.c

Package	Version	Supposed error message	Full log
libkcapi	1.0.3-2	clang: error: argument unused during compilation: '-pie' [-Werror,-Wunused-command-line-argument]	Log
librdkafka	0.11.4-1	DBG: compile check for PIC (HAVE_PIC) failed: gcc -g -O2 -fdebug-prefix-map=/<>=. -specs=/usr/share/dpkg/no-pie-compile.specs -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -I/usr/include -g -O2 -Wall -Werror _mkltmp5OVxzY.c -o _mkltmp5OVxzY.c.o -specs=/usr/share/dpkg/no-pie-link.specs -Wl,-z,relro -Wl,-z,now -L/usr/lib/x86_64-linux-gnu -fPIC: clang: error: argument unused during compilation: '-specs=/usr/share/dpkg/no-pie-compile.specs' [-Werror,-Wunused-command-line-argument]	Log
python-pyxattr	0.6.0-2	clang: error: argument unused during compilation: '-specs=/usr/share/dpkg/no-pie-compile.specs' [-Werror,-Wunused-command-line-argument]	Log
xen	4.8.3+comet2+shim4.10.0+comet3-1+deb9u5	clang: error: argument unused during compilation: '-Wa,--strip-local-absolute' [-Werror,-Wunused-command-line-argument]	Log

4 errors