"Argument unused caused failure" build failure(s) — clang 3.8.1

Unknown or unused arguments triggers errors with -Werror:
clang -Werror -ggdb3 foo.c
PackageVersionSupposed error messageFull log Bug report
libsoldout 1.4-1clang: error: argument unused during compilation: '-pie' Log
libwebsockets 1.7.3-1clang: error: argument unused during compilation: '-pie' Log
spice-vdagent 0.15.0-1.3clang: error: argument unused during compilation: '-Wp,-D_FORTIFY_SOURCE=2' Log

3 errors