Wrong printf specifiers

[stefano-zanotti]

When LFS_TRACE is enabled, some printf-like calls are compiled.
Some of the %-specifiers are wrong (they do not match the actual type of the arguments), which raises compiler warnings, possibly escalated to errors.
In two cases (see below), the specifier should be changed. In another one, a cast is needed.

In lfs.c:5889: ".block_cycles=%"PRIu32 --> PRIi32

In lfs.c:5919: ".block_cycles=%"PRIu32 --> PRIi32

In lfs.c:6078: flags --> (unsigned)flags