Remove dependencies on obsolete __ARCH_WANT_SYSCALL_NO_FLAGS syscalls.

(aarch64 kernels only have the newer system calls.)

Also expose the new functionality that's exposed by glibc in our header files.

Change-Id: I45d2d168a03f88723d1f7fbf634701006a4843c5
diff --git a/libc/arch-mips/syscalls/dup3.S b/libc/arch-mips/syscalls/dup3.S
new file mode 100644
index 0000000..6a3752c
--- /dev/null
+++ b/libc/arch-mips/syscalls/dup3.S
@@ -0,0 +1,23 @@
+/* Generated by gensyscalls.py. Do not edit. */
+
+#include <asm/unistd.h>
+    .text
+    .globl dup3
+    .align 4
+    .ent dup3
+
+dup3:
+    .set noreorder
+    .cpload $t9
+    li $v0, __NR_dup3
+    syscall
+    bnez $a3, 1f
+    move $a0, $v0
+    j $ra
+    nop
+1:
+    la $t9,__set_errno
+    j $t9
+    nop
+    .set reorder
+    .end dup3