make-seccomp-filters.sh: split cflags/ldflags for libseccomp

Resolves a link failure with -Wl,--as-needed.
Thanks to Mathias Krause for noticing the problem.

Signed-off-by: Mike Gilbert <floppym@gentoo.org>

make-seccomp-filters.sh

@@ -4,10 +4,12 @@ set -ufe
 >&2 echo YOU DO NOT NEED TO RUN IT UNLESS YOU EDITED seccomp-bpf.c
 
 : "${CC:=gcc}"
-: "${CCFLAGS:=$(pkg-config --cflags --libs libseccomp)}"
+: "${PKG_CONFIG:=pkg-config}"
+: "${SECCOMP_CFLAGS:=$(${PKG_CONFIG} --cflags libseccomp)}"
+: "${SECCOMP_LIBS:=$(${PKG_CONFIG} --libs libseccomp)}"
 
 generator="$(mktemp)"
 trap 'rm "${generator}"' EXIT
 
-"${CC}" -o "${generator}" -D_GNU_SOURCE ${CCFLAGS} seccomp-bpf.c && \
+${CC} -o "${generator}" -D_GNU_SOURCE ${SECCOMP_CFLAGS} ${CFLAGS-} ${LDFLAGS-} seccomp-bpf.c ${SECCOMP_LIBS} && \
 	"${generator}" > seccomp-bpf.h