apparmor: fix build failure on sparc caused by undeclared signals

  In file included from security/apparmor/ipc.c:23:0:
  security/apparmor/include/sig_names.h:26:3: error: 'SIGSTKFLT' undeclared here (not in a function)
    [SIGSTKFLT] = 16, /* -, 16, - */
     ^
  security/apparmor/include/sig_names.h:26:3: error: array index in initializer not of integer type
  security/apparmor/include/sig_names.h:26:3: note: (near initialization for 'sig_map')
  security/apparmor/include/sig_names.h:51:3: error: 'SIGUNUSED' undeclared here (not in a function)
    [SIGUNUSED] = 34, /* -, 31, - */
     ^
  security/apparmor/include/sig_names.h:51:3: error: array index in initializer not of integer type
  security/apparmor/include/sig_names.h:51:3: note: (near initialization for 'sig_map')

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: c6bf1adaecaa ("apparmor: add the ability to mediate signals")
Signed-off-by: John Johansen <john.johansen@canonical.com>