stand/ficl 64-bit compatibility

Currently, the only thing that prevents a functioning 64-bit FICL build is
a few integer types that were intended to be fixed-width.

Changing them to C99 integer types allows building a functioning 64-bit
FICL.

While this isn't applicable to the default settings of any in-tree loaders,
it is necessary for a future Petitboot loader, due to the requirement that
it be compiled as a 64-bit program.

(cherry picked from commit 9e4c35f867aca020df8d01fb7371bf5ae1cc8a2d)
(cherry picked from commit 0ebbda971890c149c5028066fc5ed7ea72228d87)