Add unique syscall entry numbers (SENs)

* Makefile.am (BUILT_SOURCES, CLEANFILES): Add sen.h.
(syscallent_names, syscallent_patterns, syscallent_files): New variables.
(sen.h): New rule.
* defs.h (struct sysent): Add sen field.
* generate_sen.sh: New file.
* linux/syscall.h: Include "sen.h".
* syscall.c (SEN_NAME): New temporary macro.
(SEN): Use it to prepend syscall entry number.
diff --git a/linux/syscall.h b/linux/syscall.h
index bd70601..1b7cbc5 100644
--- a/linux/syscall.h
+++ b/linux/syscall.h
@@ -28,6 +28,7 @@
 
 #include "dummy.h"
 #include "sys_func.h"
+#include "sen.h"
 
 #if NEED_UID16_PARSERS
 extern SYS_FUNC(chown16);