prf.c: remove arbitrary large stack buffer usage

The on-stack work buffer occupies 201 bytes by default. Now that we've
made the code able to cope with virtually unlimited width and precision
values, we can reduce stack usage to its strict minimum i.e. 25 bytes.

This allows for some additional sprintf tests exercizing wide results.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
2 files changed