jvmti patch for mingw32

[Mohan Embar]

Hi Marco,

> Building for mingw32 is currently broken at multiple places. This is the 
> first patch. I'll see if I can fix the others as well...

Are the other broken places similar missing JNICALL declarations
or other issues? If they are similar missing declarations, can you
combine them into one patch? Thanks for looking into this. If you
create a proper ChangeLog, I'll check this in if no one else does.

-- Mohan
http://www.thisiscool.com/
http://www.animalsong.org/