defs.h: do not include <signal.h>

* printsiginfo.h: New file.
* Makefile.am (strace_SOURCES): Add it.
* defs.h: Do not include <signal.h>.
(printsiginfo): Remove.
* printsiginfo.c: Include <signal.h> and "printsiginfo.h".
* strace.c: Likewise.
* sigaltstack.c: Include <signal.h>.
* signal.c: Likewise.
* sigreturn.c: Likewise.
* time.c: Likewise.
diff --git a/signal.c b/signal.c
index 814c9f0..e0f2a70 100644
--- a/signal.c
+++ b/signal.c
@@ -32,6 +32,7 @@
  */
 
 #include "defs.h"
+#include <signal.h>
 
 #ifndef NSIG
 # warning NSIG is not defined, using 32