signal: work around Haiku issue with SIGBUS * lib/siglist.h: Add comment. * lib/sig2str.c (numname_table): Swap SIGBUS order, to match strsignal's favoring of SIGSEGV. * tests/test-signal.c (main): Avoid test failure. * doc/posix-headers/signal.texi (signal.h): Document the issue. Reported by Scott McCreary. Signed-off-by: Eric Blake <eblake@redhat.com>