NDK: Last cleanup of the platform headers

- fix a declaration omission in 3/<grp.h>
- add missing 8/<err.h>
- simplify 8/<stdio.h>
- update 9/ headers to the latest Bionic versions
- fix a typo in android_native_app_glue.h
- use __BEGIN_DECLS .. __END_DECLS whenever possible.
- remove C++-style comments from headers

Change-Id: I58b98b3973cde494436206194ba33416a11ca8ee

ndk/platforms/android-9/include/android/rect.h

@@ -18,9 +18,9 @@
 #ifndef ANDROID_RECT_H
 #define ANDROID_RECT_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
 
 typedef struct ARect {
     int32_t left;
@@ -29,8 +29,6 @@ typedef struct ARect {
     int32_t bottom;
 } ARect;
 
-#ifdef __cplusplus
-};
-#endif
+__END_DECLS
 
-#endif // ANDROID_RECT_H
+#endif /* ANDROID_RECT_H */