tools/nolibc/printf: Support negative variable width and precision

tools/nolibc/printf: Support negative variable width and precision

For (eg) "%*.*s" treat a negative field width as a request to left align
the output (the same as the '-' flag), and a negative precision to
request the default precision.

Set the default precision to -1 (not INT_MAX) and add explicit checks
to the string handling for negative values (makes the tet unsigned).

For numeric output check for 'precision >= 0' instead of testing
_NOLIBC_PF_FLAGS_CONTAIN(flags, '.').
This needs an inverted test, some extra goto and removes an indentation.
The changed conditionals fix printf("%0-#o", 0) - but '0' and '-' shouldn't
both be specified.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
Link: https://patch.msgid.link/20260323112247.3196-1-david.laight.linux@gmail.com
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>