Add extended attribute (xattr) system call wrappers to bionic.

The xattr system calls are required for the SE Android userspace in
order to get and set file security contexts.  In particular, libselinux
requires these calls.

Change-Id: I78f5eb3d8f3384aed0a5e7c6a6f001781d982017

libc/arch-x86/syscalls/getxattr.S

@@ -0,0 +1,32 @@
+/* autogenerated by gensyscalls.py */
+#include <sys/linux-syscalls.h>
+
+    .text
+    .type getxattr, @function
+    .globl getxattr
+    .align 4
+
+getxattr:
+    pushl   %ebx
+    pushl   %ecx
+    pushl   %edx
+    pushl   %esi
+    mov     20(%esp), %ebx
+    mov     24(%esp), %ecx
+    mov     28(%esp), %edx
+    mov     32(%esp), %esi
+    movl    $__NR_getxattr, %eax
+    int     $0x80
+    cmpl    $-129, %eax
+    jb      1f
+    negl    %eax
+    pushl   %eax
+    call    __set_errno
+    addl    $4, %esp
+    orl     $-1, %eax
+1:
+    popl    %esi
+    popl    %edx
+    popl    %ecx
+    popl    %ebx
+    ret