Support 32-bit ARM vdso.

Linux 4.1 added this.

Bug: http://b/19198045
Change-Id: I28be802ff403a61dd6733a001411b3ff05fef5a5
diff --git a/libc/bionic/vdso.cpp b/libc/bionic/vdso.cpp
index 029c148..f3d95ca 100644
--- a/libc/bionic/vdso.cpp
+++ b/libc/bionic/vdso.cpp
@@ -17,7 +17,7 @@
 #include "private/bionic_globals.h"
 #include "private/bionic_vdso.h"
 
-#if defined(__aarch64__) || defined(__x86_64__) || defined (__i386__)
+#if defined(__aarch64__) || defined(__arm__) || defined(__i386__) || defined(__x86_64__)
 
 #include <limits.h>
 #include <link.h>
@@ -28,6 +28,8 @@
 #include <unistd.h>
 #include "private/KernelArgumentBlock.h"
 
+#define AT_SYSINFO_EHDR 33 /* until we have new enough uapi headers... */
+
 int clock_gettime(int clock_id, timespec* tp) {
   auto vdso_clock_gettime = reinterpret_cast<decltype(&clock_gettime)>(
     __libc_globals->vdso[VDSO_CLOCK_GETTIME].fn);