I suspect that jni.h is trying to #include <jni_md.h>, which is then failing because you haven’t added its location to your include path.
Try adding both of these entries to your C compiler’s include path:
C:\Program Files\Java\jdk1.7.0\includeC:\Program Files\Java\jdk1.7.0\include\win32
The win32 path might not be necessary, depending on how jni.h is set up.