Move away from the __ARCH_WANT_SYSCALL_NO_AT system calls.

Modern architectures only get the *at(2) system calls. For example,
aarch64 doesn't have open(2), and expects userspace to use openat(2)
instead.

Change-Id: I87b4ed79790cb8a80844f5544ac1a13fda26c7b5
diff --git a/libc/arch-arm/syscalls/mknodat.S b/libc/arch-arm/syscalls/mknodat.S
new file mode 100644
index 0000000..4a64eea
--- /dev/null
+++ b/libc/arch-arm/syscalls/mknodat.S
@@ -0,0 +1,16 @@
+/* Generated by gensyscalls.py. Do not edit. */
+
+#include <asm/unistd.h>
+#include <linux/err.h>
+#include <machine/asm.h>
+
+ENTRY(mknodat)
+    mov     ip, r7
+    ldr     r7, =__NR_mknodat
+    swi     #0
+    mov     r7, ip
+    cmn     r0, #(MAX_ERRNO + 1)
+    bxls    lr
+    neg     r0, r0
+    b       __set_errno
+END(mknodat)