loader: For the mini-stdio we have for lua, #define them to something else

To make it easier to port lua and some of the lua modules, we have a
series of routines to implement the stdio routines, even though we don't
normally implement them in the boot loader. Add a comment to this effect.

Also, some tools, like sanitizers and static analysis tools, make
unwarranted assumptions about these, so #define them to a different name
so they stop.

Sponsored by: Netflix

(cherry picked from commit 9a5aaa97cbae024f90bb626f78c3dbde28653c58)