Deal with architectures which haven't implemented openat() yet

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/klibc/openat.c b/klibc/openat.c
index b8ae053..2975112 100644
--- a/klibc/openat.c
+++ b/klibc/openat.c
@@ -10,7 +10,7 @@
 #include <fcntl.h>
 #include <bitsize.h>
 
-#if _BITSIZE == 32 && !defined(__i386__)
+#if _BITSIZE == 32 && !defined(__i386__) && defined(__NR_openat)
 
 extern int __openat(int, const char *, int, mode_t);