[sanitizer] Define SANITIZER_USE_GETAUXVAL for Android

[cryptoad]

Summary

Android for API level >= 21 has getauxval. Enable SANITIZER_USE_GETAUXVAL
when those requirements are met. Correct a typo in the header.

lib/sanitizer_common/sanitizer_getauxval.h

 //===-- sanitizer_getauxval.h -----------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Common getauxval() guards and definitions.
-// getauxval() is not defined until glbc version 2.16.
+// getauxval() is not defined until glibc version 2.16, or until API level 21
+// for Android.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef SANITIZER_GETAUXVAL_H
 #define SANITIZER_GETAUXVAL_H
 
 #include "sanitizer_platform.h"
 
 #if SANITIZER_LINUX
 
 #include <features.h>
 
 #ifndef __GLIBC_PREREQ
 #define __GLIBC_PREREQ(x, y) 0
 #endif
 
-#if __GLIBC_PREREQ(2, 16)
+#if __GLIBC_PREREQ(2, 16) || (SANITIZER_ANDROID && __ANDROID_API__ >= 21)
 # define SANITIZER_USE_GETAUXVAL 1
 #else
 # define SANITIZER_USE_GETAUXVAL 0
 #endif
 
 #if SANITIZER_USE_GETAUXVAL
 #include <sys/auxv.h>
 #endif
 
 #endif // SANITIZER_LINUX
 
 #endif // SANITIZER_GETAUXVAL_H