jni.h can't be included by C/C++ libraries

Hello,

I noticed that in a recent commit, support for JNI .cc files—originally intended to be shared between Android and iOS was removed. Specifically, the following section in `J2ObjC_types.h` was deleted:
```
#if defined(__OBJC__) || defined(__cplusplus__)
typedef bool jboolean;
#else
typedef uint8_t jboolean;
#endif
...
typedef _Atomic(jboolean) volatile_jboolean;
```

From my understanding, the project is expected to maintain backward compatibility with native code used in other projects. Could you please clarify whether this removal was intentional, and if so, what the recommended approach is for maintaining cross-platform JNI compatibility going forward?

Thank you.