src/privsep-linux: fix build on sparc (#26)

src/privsep-linux: fix build on sparc (#26)

Fix the following build failure:

privsep-linux.c:203: warning: "AUDIT_ARCH_SPARC64" redefined
  203 | #    define AUDIT_ARCH_SPARC64
      |
In file included from privsep-linux.c:35:
/srv/storage/autobuild/run/instance-0/output-1/host/sparc64-buildroot-linux-gnu/sysroot/usr/include/linux/audit.h:392: note: this is the location of the previous definition
  392 | #define AUDIT_ARCH_SPARC64 (EM_SPARCV9|__AUDIT_ARCH_64BIT)
      |
In file included from privsep-linux.c:36:
privsep-linux.c:215:38: error: 'SECCOMP_AUDIT_ARCH' undeclared here (not in a function); did you mean 'SECCOMP_ALLOW_ARG'?
  215 |  BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SECCOMP_AUDIT_ARCH, 1, 0),
      |                                      ^~~~~~~~~~~~~~~~~~

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>