common: leave any breadcrumbs when _link_out_file_named can't find the output file

common: leave any breadcrumbs when _link_out_file_named can't find the output file

_link_out_file_named is an obnoxiously complicated helper involving a
perl script embedded inside a bash subshell that does ... a lookup of
some sort involving comparing the comma-separated list in its second
argument against a comma-separated list in a config file that then maps
to an output file suffix.  I don't know what it really does.  The .cfg
file format is undocumented except for the perl script.

This is really irritating every time I have to touch any of these tests
with flexible golden outputs, and I frequently screw up the mapping.
The helper is not very helpful when you do this, because it doesn't even
try to tell you *which* suffix it found, let alone how it got there.

Fix this up so that the .full file gets some diagnostics, even if the
stdout text is "no qualified output".

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zorro Lang <zlang@kernel.org>