Modernize: use sigaction() whenever possible. Remove uses of common.

bsd_signal() may not be defined, and there is really no reason to even
try to use it if sigaction() is avaiable; using sigaction() guarantees
the semantics we really want.

Replace uses of common variables with explicit instantiation and
extern declarations in a header file.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

lib/Makefile

@@ -25,5 +25,3 @@ libxtra.a: $(LIBOBJS)
 	-rm -f libxtra.a
 	$(AR) libxtra.a $(LIBOBJS)
 	$(RANLIB) libxtra.a
-
-

lib/bsdsignal.c

@@ -1,27 +0,0 @@
-/*
- * bsdsignal.c
- *
- * Use sigaction() to simulate BSD signal()
- */
-
-#include "config.h"
-
-void (*bsd_signal(int signum, void (*handler) (int))) (int) {
-    struct sigaction action, oldaction;
-
-    memset(&action, 0, sizeof action);
-    action.sa_handler = handler;
-    sigemptyset(&action.sa_mask);
-    sigaddset(&action.sa_mask, signum);
-    action.sa_flags = SA_RESTART;
-
-    if (sigaction(signum, &action, &oldaction) == -1) {
-#ifdef SIG_ERR
-        return SIG_ERR;
-#else
-        return NULL;
-#endif
-    }
-
-    return oldaction.sa_handler;
-}