Add preadv/pwritev.

Bug: http://b/12612572
Change-Id: I38ff2684d69bd0fe3f21b1d371b88fa60d5421cb
diff --git a/libc/arch-mips/syscalls/__pwritev64.S b/libc/arch-mips/syscalls/__pwritev64.S
new file mode 100644
index 0000000..1222942
--- /dev/null
+++ b/libc/arch-mips/syscalls/__pwritev64.S
@@ -0,0 +1,19 @@
+/* Generated by gensyscalls.py. Do not edit. */
+
+#include <private/bionic_asm.h>
+
+ENTRY(__pwritev64)
+    .set noreorder
+    .cpload t9
+    li v0, __NR_pwritev
+    syscall
+    bnez a3, 1f
+    move a0, v0
+    j ra
+    nop
+1:
+    la t9,__set_errno_internal
+    j t9
+    nop
+    .set reorder
+END(__pwritev64)