add sigaltstack syscall
diff --git a/libc/include/sys/linux-unistd.h b/libc/include/sys/linux-unistd.h
index f48dbcd..d6f706b 100644
--- a/libc/include/sys/linux-unistd.h
+++ b/libc/include/sys/linux-unistd.h
@@ -48,6 +48,7 @@
int prctl (int option, unsigned int arg2, unsigned int arg3, unsigned int arg4, unsigned int arg5);
int capget (cap_user_header_t header, cap_user_data_t data);
int capset (cap_user_header_t header, const cap_user_data_t data);
+int sigaltstack (const stack_t*, stack_t*);
int acct (const char* filepath);
ssize_t read (int, void*, size_t);
ssize_t write (int, const void*, size_t);