fflag to ignore fts_read errors, but stop deleting from that directory
because no further progress can be made.
When building a kernel with a high -j value on a high core count
machine, during the cleanobj phase we can wind up doing multiple rm
-rf at the same time for modules that have subdirectories. This
exposed this race (sometimes) as fts_read can return an error if the
directory is removed by another rm -rf. Since the intent of the -f
flag was to ignore errors, even if this was a bug in fts_read, we
should ignore the error like we've been instructed to do.
413a368c90