Declare syscall parsers using SYS_FUNC macro

Introduce SYS_FUNC macro to declare and define all syscall parsers.

* Makefile.am (BUILT_SOURCES, CLEANFILES): Add sys_func.h.
(sys_func.h): New rule.
* defs.h (SYS_FUNC_NAME, SYS_FUNC): New macros.
* linux/syscall.h: Include "sys_func.h".
[NEED_UID16_PARSERS]: Use SYS_FUNC to declare uid16 syscall parsers.
Remove other declarations.
* linux/alpha/syscallent.h (160, 161): Add sys_ prefix to osf_statfs
and osf_fstatfs syscall parsers.
* *.c: Use SYS_FUNC to define syscall parsers.
diff --git a/umask.c b/umask.c
index cc00cc6..9b50385 100644
--- a/umask.c
+++ b/umask.c
@@ -1,7 +1,6 @@
 #include "defs.h"
 
-int
-sys_umask(struct tcb *tcp)
+SYS_FUNC(umask)
 {
 	if (entering(tcp)) {
 		tprintf("%#lo", tcp->u_arg[0]);