In Android's NDK16, jobject is now declared as:
    #ifdef __cplusplus
    class _jobject {};
    typedef _jobject*       jobject;
    #else /* not __cplusplus */
    typedef void*           jobject;
    #endif

This makes the jobject to uintptr check fail because it expects the
following definition:
    struct _jobject;
    typedef struct _jobject *jobject;

Update the type check to handle that new type definition in both C and
C++ modes.

Fixes #26213

Change-Id: Ic36d4a5176526998d2d5e4e404f8943961141f7a
GitHub-Last-Rev: 42037c3c584579c2b3281c25372b830e864e7aec
GitHub-Pull-Request: golang/go#26221
Reviewed-on: https://go-review.googlesource.com/122217
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>