Don't define |r_debug| and |link_map| on Android releases 21 and later

src/common/android/include/link.h

Index: src/common/android/include/link.h
diff --git a/src/common/android/include/link.h b/src/common/android/include/link.h
index e7ff8e2d8702b0037921b50c99b94f02758f6e2a..c8c217631894868c07d65d7f54c6ae70e19d6bc5 100644
--- a/src/common/android/include/link.h
+++ b/src/common/android/include/link.h
@@ -43,6 +43,8 @@
 extern "C" {
 #endif  // __cplusplus
 
+// The structures below are present in ndk 21 and later.
+#if defined(ANDROID) && ANDROID_VERSION <= 20

[rmcilroy, 2016/07/18 15:04:08]

I don't think the defined(ANDROID) is needed - these headers are only included
if building for Android. 

Also, where does ANDROID_VERSION come from? I don't think it is defined in the
NDK and we don't define it either in Breakpad or Chromium's build as far as I
can tell.

Instead you might have to do something like what's done in elf.h where we do,
for example:
#define Elf32_auxv_t  __bionic_Elf32_auxv_t
#define Elf64_auxv_t  __bionic_Elf64_auxv_t

Then undef this definition and redefine the structs here.

 struct r_debug {
   int              r_version;
   struct link_map* r_map;
@@ -61,6 +63,7 @@ struct link_map {
   struct link_map* l_next;
   struct link_map* l_prev;
 };
+#endif
 
 #ifdef __cplusplus
 }  // extern "C"