add prototypes for GNU *_unlocked stdio functions
add prototypes for GNU *_unlocked stdio functions

actually these are just weak aliases for the normal locking versions
right now, and they will probably stay that way since making them
lock-free without slowing down the normal versions would require
significant code duplication for no benefit.

chardi/musl,davidlazar/musl,davidlazar/musl,chardi/musl,chardi/musl