Add *int64 and GLsync types and related functions

Return values are declared with the C return type, but the JNI
function returns the JNI return type. In the case of GLsync/jlong as
in glFenceSync(), this causes a compile error. So the generator now
explicitly casts the return value to the JNI return type.

Bug: 8566953
Change-Id: I814befe2e4cce745434cbc4e1c8639fc3ce8aeae