"Argument unused caused failure" build failure(s) — clang 3.6.0

Unknown or unused arguments triggers errors with -Werror:
clang -Werror -ggdb3 foo.c
PackageVersionSupposed error messageFull log Bug report
criu 1.3.1-1clang: error: argument unused during compilation: '-Wa,--noexecstack' Log 753845
dwb 20140702hg-2clang: error: argument unused during compilation: '--ansi' Log
libwebsockets 1.2.2-1clang: error: argument unused during compilation: '-rdynamic' Log
policycoreutils 2.3-1clang: error: argument unused during compilation: '-shared' Log
spice-vdagent 0.15.0-1.2clang: error: argument unused during compilation: '-Wp,-D_FORTIFY_SOURCE=2' Log

5 errors