libc: Add missing pipe2() declaration and implementation.

Change-Id: Iacb914bd6ac5adc60c5671e6fef680ede21f9b0c
diff --git a/libc/arch-arm/syscalls/pipe2.S b/libc/arch-arm/syscalls/pipe2.S
new file mode 100644
index 0000000..df77094
--- /dev/null
+++ b/libc/arch-arm/syscalls/pipe2.S
@@ -0,0 +1,19 @@
+/* autogenerated by gensyscalls.py */
+#include <sys/linux-syscalls.h>
+
+    .text
+    .type pipe2, #function
+    .globl pipe2
+    .align 4
+    .fnstart
+
+pipe2:
+    .save   {r4, r7}
+    stmfd   sp!, {r4, r7}
+    ldr     r7, =__NR_pipe2
+    swi     #0
+    ldmfd   sp!, {r4, r7}
+    movs    r0, r0
+    bxpl    lr
+    b       __set_syscall_errno
+    .fnend