Now with DISABLE_DYNLOADING, SAL_DLLPUBLIC_EXPORT actually means
hidden visibilty. Which is OK in general as with a single DSO (or a
single executable, for iOS), none of our "normal" entry points need to
be visible froom the outside.

So for the JNI entry points use JNIEXPORT. On "normal" platforms it
should be equivalent to SAL_DLLPUBLIC_EXPORT.

Change-Id: Iad634950e635ac03a0e90cae6d00afd9fb4eeb64