Move default PTRACE_ constants into new file trace-defs.h

Include it also in events.c, where we use them as well.
diff --git a/sysdeps/linux-gnu/trace.c b/sysdeps/linux-gnu/trace.c
index 929808b..e13b761 100644
--- a/sysdeps/linux-gnu/trace.c
+++ b/sysdeps/linux-gnu/trace.c
@@ -38,6 +38,7 @@
 #endif
 
 #include "linux-gnu/trace.h"
+#include "linux-gnu/trace-defs.h"
 #include "backend.h"
 #include "breakpoint.h"
 #include "debug.h"
@@ -47,33 +48,6 @@
 #include "ptrace.h"
 #include "type.h"
 
-/* If the system headers did not provide the constants, hard-code the normal
-   values.  */
-#ifndef PTRACE_EVENT_FORK
-
-#define PTRACE_OLDSETOPTIONS    21
-#define PTRACE_SETOPTIONS       0x4200
-#define PTRACE_GETEVENTMSG      0x4201
-
-/* options set using PTRACE_SETOPTIONS */
-#define PTRACE_O_TRACESYSGOOD   0x00000001
-#define PTRACE_O_TRACEFORK      0x00000002
-#define PTRACE_O_TRACEVFORK     0x00000004
-#define PTRACE_O_TRACECLONE     0x00000008
-#define PTRACE_O_TRACEEXEC      0x00000010
-#define PTRACE_O_TRACEVFORKDONE 0x00000020
-#define PTRACE_O_TRACEEXIT      0x00000040
-
-/* Wait extended result codes for the above trace options.  */
-#define PTRACE_EVENT_FORK       1
-#define PTRACE_EVENT_VFORK      2
-#define PTRACE_EVENT_CLONE      3
-#define PTRACE_EVENT_EXEC       4
-#define PTRACE_EVENT_VFORK_DONE 5
-#define PTRACE_EVENT_EXIT       6
-
-#endif /* PTRACE_EVENT_FORK */
-
 void
 trace_fail_warning(pid_t pid)
 {