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-mips/syscalls/mknodat.S b/libc/arch-mips/syscalls/mknodat.S
new file mode 100644
index 0000000..fc05bb3
--- /dev/null
+++ b/libc/arch-mips/syscalls/mknodat.S
@@ -0,0 +1,23 @@
+/* Generated by gensyscalls.py. Do not edit. */
+
+#include <asm/unistd.h>
+    .text
+    .globl mknodat
+    .align 4
+    .ent mknodat
+
+mknodat:
+    .set noreorder
+    .cpload $t9
+    li $v0, __NR_mknodat
+    syscall
+    bnez $a3, 1f
+    move $a0, $v0
+    j $ra
+    nop
+1:
+    la $t9,__set_errno
+    j $t9
+    nop
+    .set reorder
+    .end mknodat